Curiosities of the sky

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GREAT SPIRAL NEBULA IN ANDROMEDA

CURIOSITIES
OF THE SKY

A POPULAR PRESENTATION OF THE
GREAT RIDDLES AND MYSTERIES OF

ASTRONOMY

BY

GARRETT P. SERVISS

AUTHOR OF

" ASTRONOMY' WITH THE NAKED EYE"
"ASTRONOMY WITH AN OPEKA-GLASS "

ETC. ETC.

WITH MANY ILLUSTRATIONS FROM
PHOTOGRAPHS AND DRAWINGS

NEW YORK AND LONDON
HARPER & BROTHERS PUBLISHERS

UBUAY

BOOKS BY
GARRETT P. SERVISS

THE MOON METAL. Post 8vo
ASTRONOMY WITH THE NAKED EYE

Illustrated. Post 8vo

CURIOSITIES OF THE SKY. Illustrated. 8vo
ROUND THE YEAR WITH THE STARS

Illustrated. 8vo
ELOQUENCE. Post 8vo

HARPER & BROTHERS, NEW YORK

Copyright, 1909, by HARPER & BROTHERS.

Published November, 1909.
Printed in the United States of America

555

CONTENTS
i

THE WINDOWS OF ABSOLUTE NIGHT

On the edges of the universe — The mystery of the " Coal-sacks" —
Description of the great "Coal-sack" in the "Southern Cross"
— Its effect upon the imagination — The "Coal-sack" in Cygnus
— Photographic discovery of apparent apertures in the Milky
Way — Strange lanes among the stars — Professor Barnard's
theory of "Dark Nebulae" — The problem of the extinction
of light in space — If the "Coal -sacks" are openings in the walls
of the universe, what lies beyond? — Inconceivability of an
end to space — The universe not a Crusoe lost in immensity —
Reasons for thinking that other universes exist — What is their
probable appearance? — Will any of them ever be seen from
our starry system? — Does the luminiferous ether extend
throughout infinite space? Page i

II
STAR-CLOUDS, STAR-CLUSTERS, AND STAR-STREAMS

The Milky Way the most stupendous of all astronomical phe-
nomena— The strange ground-plan of the universe — A chaplet
of a hundred million suns — An extraordinary speculation con-
cerning the nature of the Galaxy — Professor Comstock's "star-
plough" — The wonderful details of the Milky Way — Distinc-
tion between star-clouds, star-swarms, and star-clusters — The
mystery of the globular star-clusters — The " Great Cluster in
Hercules" and the still richer one in Centaurus — How did the
stars in dense clusters come together ? — The startling idea of an
explosion — The wonderful association of stars and nebulas
in the Pleiades — Nebulous "rail fences" with strange banks
of stars arrayed along them ........ Page 17

507

CONTENTS

III
STELLAR MIGRATIONS

The paradox of the " fixed stars" — All is motion in the universe —
Extraordinary speed of some "runaway stars" — The fearful
momentum of Arcturus — What is to become of stars whose
motion is so swift that the attractions of the universe cannot
govern them? — Stars travelling in groups — The motion of the
solar system — Whence have we come, and whither do we go?
— Enormous spaces that the earth has traversed during the
geologic ages — Curious thoughts suggested by this stupendous
voyage — Shall we eventually join the Milky Way? — The ex-
traordinary theory of a double drift of the stars — Is the stellar
system divided into two opposed streams? — Stars moving like
snow-flakes driven before interpenetrating winds . . Page 39

IV
THE PASSING OF THE CONSTELLATIONS

How time affects the blazonry of the heavens — The constellations
and human tradition — The most lasting records of men's
thoughts — The constellations and religion — American tradi-
tions— The wonderful impression made by Greek tradition as
preserved in the stars — The effects of the stellar motions in
difforming the constellations— When the "Great Dipper"
will no longer hold water — Curious results of star-drift in the
"Northern Crown" — The Hyades drifting apart — Famous
star figures, full of poetic suggestion, which cannot last — Orion,
the " Mighty Hunter," stands almost unchanged, but his " belt"
is falling to pieces — The curious fate that attends the beautiful
"Southern Cross" — Future mythologies must invent new
constellations — The sun among the constellations seen from
distant space Page 53

V
CONFLAGRATIONS IN THE HEAVENS

The burning up of the earth would be a catastrophe invisible
from stellar space — Yet many great outbursts of light have
appeared to us among the stars — The phenomena of new or
temporary stars — The famous star of Tycho — The legend that

vi

CONTENTS

it was a reappearance of the "Star of Bethlehem" — Kepler's
star, and other fiery outbursts — The great new star of 1901,
"Nova Persei," and the light it has thrown on such phenomena
— Extraordinary theories based upon it — Was it the result of a
collision ? — How suns may be a source of danger to each other
without coming into actual collision — The theory of an en-
counter between a star and a "dark nebula" — Suggestion of
the "running down" of planets by an invading star — Janssen's
theory of explosive chemical action — How temporary stars
appear to run through the stages of stellar history in a few
months — Significance of their changes of color. . Page 68

VI
EXPLOSIVE AND WHIRLING NEBULAE

Professor Keeler's surprising discovery that most of the nebulas
are spiral in form — The effect of this discovery on Laplace's
Nebular Hypothesis — Immense variety of the spiral forms —
Is Laplace's hypothesis still applicable, with modifications, to
our particular system? — Suggestive forms of "rings" and
" planetary " nebulae — The marvels revealed by photography
in Lord Rosse's " Whirlpool," and the amazing spectacle pre-
sented by a spiral nebula in Triangulum — Other strange
forms — The wonderful Andromeda Nebula — The mystery of
the "white" nebulae — The chaotic gaseous nebula in Orion —
Suggestive arrangement accompanying stars — Are these nebulae
the birthplaces of star-clusters? — The new " Planetesimal Hy-
pothesis," and the astonishing view of the origin of solar sys-
tems that it offers — Do we yet know the real truth ? . Page 88

VII
THE BANNERS OF THE SUN

The wonderful surroundings of the sun that only an eclipse re-
veals— The dramatic story of the first scientific observation of
the corona and the prominences of the sun — The coronas of
1900 and 1905 — The curved rays about the solar poles resem-
bling the lines of force of a magnet — Solar magnetic influence
upon the earth — The phenomena of the eruptive prominences
— Does the sun hurl forth masses of matter that reach the
planets? — Connection of the prominences and the corona with
sun-spots — The remarkable results of the "pressure of light" —
The sun-spot period and "magnetic storms" — The sun a

vii

CONTENTS

variable star — How its light is partially cut off by absorbing
vapors — Once it probably shone more brilliantly than it does
at the present time Page 113

VIII
THE ZODIACAL LIGHT MYSTERY

The ghostly presence that towers above the sunken sun — The
light varies in appearance with the seasons — How it looks in
the tropics and upon the equator — Humboldt's observations —
The Zodiacal Light in 1909 — The writer's observations — The
curious "Gegenschein" — Professor Barnard's observations — The
Rev. Mr. Jones' round the world studies of the Zodiacal Light
— The extraordinary theory of Arrhenius — Once more the
pressure of light — How negatively charged corpuscles driven
from the sun are conceived to envelop the earth and produce
the appearance of the Zodiacal Light — The theories of coronal
extension and of clouds of meteors — Why an airless planet
cannot have comets' tails as the earth is supposed to
have Page 131

IX
MARVELS OF THE AURORA

An amazing spectacle that recalled pictures of "The Day of
Judgment" — The aurora of 1882, and the strange upright
beam that appeared stalking across the sky — Auroras in the
Arctic and Antarctic regions — Their connection with the
magnetic poles — The earth as a great magnet — Astonishing
phenomenon observed in 1859 — Outbursts on the sun followed
by extraordinary auroral displays and magnetic storms on the
earth — Lord Kelvin's objection, and the answer to it — Proofs
of the intimate connection between solar outbreaks and terres-
trial disturbances — Another application of the theory of
Arrhenius — Negative particles shot from the sun supposed to
electrify the earth's atmosphere and thus to produce the
play of the auroral lights — Curious confirmations of the
theory Page 144

X
STRANGE ADVENTURES OP COMETS

How the fears and , superstitions of ancient times have been suc-
ceeded by scientific study of comets — An account of the

viii

CONTENTS

characteristic phenomena of a comet — Science itself has dis-
covered mysteries — How the nuclei and tails of comets are
developed — The chemical constituents of comets — Remarkable
comets of the nineteenth century — The monster of space that
looked at us afar off in 1729 — The great comet of i8n, and
its enormous tail — In 1843 a comet was visible in broad day
beside the sun — The beautiful comet of 1858, and its supposed
connection with the wine crop — Astonishing association of
the comets of 1843, 1880, and 1882 — Three pieces of one orig-
inal mass — The disintegration of the head of the comet of
J882 — Professor Forbes' theory that these comets were split
up by the action of a yet undiscovered planet beyond Neptune —
Strange adventures of Lexell's comet — Arrhenius' theory of
the origin of comets' tails — Driven off by the pressure of light —
Jupiter as the great comet-catcher — Do comets ever come into
the solar system from interstellar space, or are they originally
carried along in the same " current" that bears onward the sun
and the planets? Page 165

XI
METEORS, FIRE-BALLS, AND METEORITES

The terrorizing spectacle of 1833 and its connection with a dis-
integrated comet — The "umbrella of fire" and the light that
it cast on the meaning of the amazing display — Olmstead's and
Schiaparelli's investigations — Meteor-swarms travel in the
tracks of comets — The tragic fate of Biela's comet — Why the
November spectacle failed in 1899 — The distinction between
meteors and meteorites — Stone meteorites and iron meteorites
— Former incredulity of men of science concerning stones fall-
ing from the sky — Showers of stones — Famous meteorites of
ancient times — Nickel-iron from the sky — Diamonds in me-
teorites— Do such bodies come from the sun or the stars, or
have they been shot out from lunar volcanoes? — The mystery
of Coon Butte — Was the crater in Arizona made by a falling
meteorite? Page 186

XII
THE WRECKING OF THE MOON

A "fossil world" in the sky — Unique character of the lunar
scenery — The story of disaster that the moon carries sculptured

ix

CONTENTS

on its face — Gigantic size of the craters of the moon — How
they differ from the volcanic craters of the earth — Some strik-
ing comparisons of magnitude — How the slight force of lunar
gravity may account for the gigantic dimensions of the craters
— The theory that they may have been formed by meteoric
impact — The question of former life on the moon — The uni-
versality of the destruction wrought by the volcanoes — The
puzzle of the ancient sea beds — Were they once floods of molten
lava? — Mr. Ritchey's wonderful photographs and their revela-
tions— Suggestions of a double tragedy in the career of the
lunar world — Ruin beneath ruin recalling the strata of buried
cities in the mound of ancient Troy Page 213

XIII
THE GREAT MARS PROBLEM

Life not ubiquitous, though probably present in all quarters of
the universe — The life question in the solar system — Why Mars
has been selected as the most probable abode of life among
the other planets — The principal facts known about Mars —
Its singular resemblances to the earth, and its no less remark-
able differences from our planet — The discoveries of Schiaparelli
and Lowell — The problematical "canals," their peculiarities,
and the interpretation that has been put upon them — Mars
a half-dried-up world — The wonderful struggle to retain life
which is ascribed to its inhabitants — Their possibly gigantic
size, and the reasons which have been given for thinking that
they may be more advanced than we are — Mr. Lowell's theory
of life on Mars — Public works that put the utmost achieve-
ments of man to shame — Objections, and the answers to
them Page 237

XIV
THE RIDDLE OP THE ASTEROIDS

A ring of little worlds where astronomers expected to find a single
large one — Olbers' startling hypothesis of a planetery explosion
— Measures of the four largest asteroids — The objections to the
explosion hypothesis, and the support which it seems to derive
from the probable abnormal shapes of Eros and others —
The theory of a series of explosions — How could a world ex-
plode?— Evidences of explosive forces in nature — The ex-

X

CONTENTS

traordinary ideas of Doctor Le Bon concerning the results of
atomic disintegration — The phenomena of the radium group of
elements appealed to in support of the hypothesis that worlds
may blow up when they have grown very old — This, says
Doctor Le Bon, may represent the most general ending of the
bodies composing the universe Page 254

INDEX 265

ILLUSTRATIONS

GREAT SPIRAL NEBULA IN ANDROMEDA Frontispiece

THE MILKY WAY Facing p. 4

STAR-CLUSTER IN HERCULES " 26

GREAT SOUTHERN STAR-CLUSTER, OMEGA CENTAURI . " 30

THE PLEIADES " 34

THE "GREAT DIPPER" Page 58

CASSIOPEIA " 60

THE "NORTHERN CROWN" " 63

THE "SOUTHERN CROSS" " 65

CHART SHOWING LOCATION OF TYCHO's STAR, 1572, AND

NOVA PERSEI OF IQOI Facing p. 70

NOVA PERSEI, WITH ITS NEBULAR RINGS . . . . " 80

LORD ROSSE'S NEBULA " 88

WONDERFUL SPIRAL IN TRIANGULUM " 92

SPIRAL IN URSA MAJOR 96

NEBULA IN CETUS IOO

THE ORION NEBULA 104

THE CORONA 1 14

A SOLAR "PROMINENCE" 120

AURORAL BEAMS SEEN IN ENGLAND 144

AURORAL ARCHES OF AN ELLIPTIC FORM SEEN IN THE

ARCTIC REGIONS 148

AURORAL CURTAIN SEEN IN SCANDINAVIA .... 154

AURORAL ARCHES SEEN IN SCANDINAVIA " 160

SWIFT'S COMET 166

xiii

ILLUSTRATIONS

DANIELS' COMET Facingp. 176

BROOKS' COMET " 180

CURIOUS FORMS OF METEORITE TRAINS " 188

SECTION OF THE ATMOSPHERE UP TO IOO KILOMETERS . " IQ2

A METEOR PHOTOGRAPHED IN FLIGHT " 198

LOOKING ACROSS COON BUTTE CRATER FROM NORTHERN

RIM *' 204

TRAIL ON SOUTH SIDE, COON BUTTE CRATER ..." 2o8

THE CRATERS CLAVIUS, LONGOMONTANUS, TYCHO, ETC. " 2l6

WESTERN PART OF THE MARE SERENITATIS .... '* 222

MARE TRANQUILITATIS AND SURROUNDINGS .... 226

LUNAR CRATER THEOPHILUS AND SURROUNDING REGION " 230

MARE CRISIUM " 234

SCHIAPARELLl'S CHART OF MARS, SHOWING THE SYSTEM

OP SO-CALLED CANALS " 244

PREFACE

WHAT Froude says of history is true also of
astronomy: it is the most impressive where it
transcends explanation. It is not the mathematics
of astronomy, but the wonder and the mystery that
seize upon the imagination. The calculation of an
eclipse owes all its prestige to the sublimity of its
data; the operation, in itself, requires no more mental
effort than the preparation of a railway time-table.

The dominion which astronomy has always held
over the minds of men is akin to that of poetry; when
the former becomes merely instructive and the latter
purely didactic, both lose their power over the imag-
ination. Astronomy is known as the oldest of the
sciences, and it will be the longest-lived because it will
always have arcana that have not been penetrated.

Some of the things described in this book are little
known to the average reader, while others are well
known; but all possess the fascination of whatever is
strange, marvellous, obscure, or mysterious — magni-
fied, in this case, by the portentous scale of the
phenomena.

The idea of the author is to tell about these things
in plain language, but with as much scientific accuracy

xv

PREFACE

as plain language will permit, showing the wonder
that is in them without getting away from the facts.
Most of them have hitherto been discussed only in
technical form, and in treatises that the general
public seldom sees and never reads.

Among the topics touched upon are: The strange
unfixedness of the "fixed stars," the vast migrations
of the suns and worlds constituting the universe;
The slow passing out of existence of those collocations
of stars which for thousands of years have formed
famous " constellations," preserving the memory of
mythological heroes and heroines, and perhaps of
otherwise unrecorded history; The tendency of stars
to assemble in immense clouds, swarms, and clusters;
The existence in some of the richest regions of the
universe of absolutely black, starless gaps, deeps,
or holes, as if one were looking out of a window into
the murkiest night; The marvellous phenomenon of
new, or temporary, stars, which appear as suddenly
as conflagrations, and often turn into something else
as eccentric as themselves; The amazing forms of the
"whirlpool," "spiral," "pinwheel," and "lace," or
"tress," nebulae; The strange surroundings of the sun,
only seen in particular circumstances, but evidently
playing a constant part in the daily phenomena of
the solar system; The mystery of the Zodiacal Light
and the Gegenschein; The extraordinary transforma-
tions undergone by comets and their tails ; The prodi-
gies of meteorites and masses of stone and metal
fallen from the sky; The cataclysms that have
wrecked the moon; The problem of life and intelli-
gence on the planet Mars; The problematical origin

xvi

PREFACE

and fate of the asteroids; and The strange phenom-
ena of the auroral lights.

An attempt has been made to develop these topics
in an orderly way, showing their connection, so that
the reader may obtain a broad general view of the
chief mysteries and problems of astronomy, and an
idea of the immense field of discovery which still lies,
almost unexplored, before it.

CURIOSITIES OF THE SKY

CURIOSITIES OF THE SKY

THE WINDOWS OF ABSOLUTE NIGHT

most minds mystery is more fascinating than
science. But when science itself leads straight
up to the borders of mystery and there comes to a
dead stop, saying, "At present I can no longer see
my way," the force of the charm is redoubled. On
the other hand, the illimitable is no less potent in
mystery than the invisible, whence the dramatic
effect of Keats' "stout Cortez" staring at the bound-
less Pacific while all his men look at each other with a
wild surmise, "silent upon a peak in Darien." It is
with similar feelings that the astronomer regards
certain places where from the peaks of the universe
his vision seems to range out into endless empty
space. He sees there the shore of his little isthmus,
and, beyond, unexplored immensity.

The name, "coal -sacks," given to these strange
voids is hardly descriptive. Rather they produce
upon the mind the effect of blank windows in a lonely
house on a pitch-dark night, which, when looked at
from the brilliant interior, become appalling in their

CURIOSITIES OF THE SKY

rayless murk. Infinity seems to acquire a new mean-
ing in the presence of these black openings in the sky,
for as one continues to gaze it loses its purely meta-
physical quality and becomes a kind of entity, like
the ocean. The observer is conscious that he can
actually see the beginning of its ebon depths, in
which the visible universe appears to float like an en-
chanted island, resplendent within with lights and
life and gorgeous spectacles, and encircled with
screens of crowded stars, but with its dazzling vistas
ending at the fathomless sea of pure darkness which
encloses all.

The Galaxy, or Milky Way, surrounds the borders
of our island in space like a stellar garland, and when
openings appear in it they are, by contrast, far more
impressive than the general darkness of the inter-
stellar expanse seen in other directions. Yet even
that expanse is not everywhere equally dark, for it
contains gloomy deeps discernible with careful watch-
ing. Here, too, contrast plays an important part,
though less striking than within the galactic region.
Some of Sir William Herschel's observations appear
to indicate an association between these tenebrious
spots and neighboring star-clouds and nebulae. It is
an illuminating bit of astronomical history that when
he was sweeping the then virgin heavens with his great
telescopes he was accustomed to say to his sister who,
note-book in hand, waited at his side to take down
his words, fresh with the inspiration of discovery:
"Prepare to write \ the nebulae are coming; here space
is vacant."

The most famous of the "coal-sacks," and the first

WINDOWS OF ABSOLUTE NIGHT

to be brought to general attention before astronomers
had awakened to the significance of such things, lies
adjacent to the "Southern Cross," and is truly an
amazing phenomenon. It is not alone the conspicu-
ousness of this celestial vacancy, opening suddenly in
the midst of one of the richest parts of the Galaxy,
that has given it its fame, but quite as much the super-
stitious awe with which it was regarded by the early
explorers of the South Seas. To them, as well as to
those who listened in wrapt wonder to their tales, the
"Coal-sack" seemed to possess some occult connection
with the mystic "Cross." In the eyes of the sailors
it was not a vacancy so much as a sable reality in the
sky, and as, shuddering, they stared at it, they piously
crossed themselves. It was another of the magical
wonders of the unknown South, and as such it formed
the basis of many a "wild surmise" and many a sea-
dog's yarn. Scientific investigation has not diminished
its prestige, and to-day no traveller in the southern
hemisphere is indifferent to its fascinating strangeness,
while some find it the most impressive spectacle of the
antarctic heavens.

All around, up to the very edge of the yawning gap,
the sheen of the Milky Way is surpassingly glorious;
but there, as if in obedience to an almighty edict,
everything vanishes. A single faint star is visible
within the opening, producing a curious effect upon the
sensitive spectator, like the sight of a tiny islet in the
midst of a black, motionless, waveless tarn. The di-
mensions of the lagoon of darkness, which is oval or
pear-shaped, are eight degrees by five, so that it oc-
cupies a space in the sky about one hundred and thirty

3

CURIOSITIES OF THE SKY

times greater than the area of the full moon. It
attracts attention as soon as the eye is directed toward
the quarter where it exists, and by virtue of the rarity
of such phenomena it appears a far greater wonder
than the drifts of stars that are heaped around it.
Now that observatories are multiplying in the southern
hemisphere, the great austral " Coal -sack" will, no
doubt, receive attention proportioned to its importance
as one of the most significant features of the sky.
Already at the Sydney Observatory photographs have
shown that the southern portion of this Dead Sea of
Space is not quite ''bottomless," although its northern
part defies the longest sounding lines of the astronomer.

There is a similar, but less perfect, "coal-sack" in
the northern hemisphere, in the constellation of
"The Swan," which, strange to say, also contains a
well-marked figure of a cross outlined by stars. This
gap lies near the top of the cross-shaped figure. It is
best seen by averted vision, which brings out the con-
trast with the Milky Way, which is quite brilliant
around it. It does not, however, exercise the same
weird attraction upon the eye as the southern "Coal-
sack," for instead of looking like an absolute void in
the sky, it rather appears as if a canopy of dark gauze
had been drawn over the stars. We shall see the
possible significance of this appearance later.

Just above the southern horizon of our northern
middle latitudes, in summer, where the Milky Way
breaks up into vast sheets of nebulous luminosity,
lying over and between the constellations Scorpio and
Sagittarius, there is a remarkable assemblage of
"coal-sacks," though none is of great size. One of

4

THE MILKY WAY. REGION NEAR M 8. PHOTOGRAPHED BY
PROFESSOR BARNARD

WINDOWS OF ABSOLUTE NIGHT

them, near a conspicuous star - cluster in Scorpio,
80 M, is interesting for having been the first of these
strange objects noted by Herschel. Probably it was
its nearness to 80 M which suggested to his mind the
apparent connection of such vacancies with star-
clusters which we have already mentioned.

But the most marvellous of the "coal-sacks" are
those that have been found by photography in
Sagittarius. One of Barnard's earliest and most
excellent photographs includes two of them, both in
the star-cluster 8 M. The larger, which is roughly
rectangular in outline, contains one little star, and its
smaller neighbor is lune-shaped — surely a most singu-
lar form for such an object. Both are associated with
curious dark lanes running through the clustered
stars like trails in the woods. Along the borders of
these lanes the stars are ranked in parallel rows, and
what may be called the bottoms of the lanes are not
entirely dark, but pebbled with faint stellar points.
One of them which skirts the two dark gaps and
traverses the cluster along its greatest diameter is
edged with lines of stars, recalling the alignment of the
trees bordering a French highway. This road of stars
cannot be less than many billions of miles in length!

All about the cluster the bed of the Galaxy is
strangely disturbed, and in places nearly denuded,
as if its contents had been raked away to form the
immense stack and the smaller accumulations of
stars around it. The well-known "Trifid Nebula"
is also included in the field of the photograph, which
covers a truly marvellous region, so intricate in its
mingling of nebulae, star-clusters, star-swarms, star-

7

CURIOSITIES OF THE SKY

streams, and dark vacancies that no description can
do it justice. Yet, chaotic as it appears, there is an
unmistakable suggestion of unity about it, impressing
the beholder with the idea that all the different parts
are in some way connected, and have not been for-
tuitously thrown together. Miss Agnes M. Clerke
made the striking remark that the dusky lanes in
8 M are exemplified on the largest scale in the great
rift dividing the Milky Way, from Cygnus in the north-
ern hemisphere all the way to the "Cross" in the
southern. Similar lanes are found in many other
clusters, and they are generally associated with flank-
ing rows of stars, resembling in their arrangement the
thick-set houses and villas along the roadways that
traverse the approaches to a great city.

But to return to the black gaps. Are they really
windows in the star- walls of the universe ? Some of
them look rather as if they had been made by a shell
fired through a luminous target, allowing the eye to
range through the hole into void space beyond. If
science is discreetly silent about these things, what
can the more venturesome and less responsible imag-
ination suggest? Would a huge "runaway sun," like
Arcturus, for instance, make such an opening if it
should pass like a projectile through the Milky Way ?
It is at least a stimulating inquiry. Being probably
many thousands of times more massive than the
galactic stars, such a stellar missile would not be
stopped by them, though its direction of flight might
be altered. It would drag the small stars lying close
to its course out of their spheres, but the ultimate
tendency of its attraction would be to sweep them

8

WINDOWS OF ABSOLUTE NIGHT

round in its wake, thus producing rather a star-swarm
than a vacancy. Those that were very close to it
might be swept away in its rush and become its sat-
ellites, careering away with it in its flight into outer
space ; but those that were farther off, and they would,
of course, greatly outnumber the near ones, would
tend inward from all sides toward the line of flight,'
as dust and leaves collect behind a speeding motor
(though the forces operating would be different) , and
would fill up the hole, if hole there were. A swarm
thus collected should be rounded in outline and bor-
dered with a relatively barren ring from which the
stars had been " sucked" away. In a general sense
the 8 M cluster answers to this description, but even
if we undertook to account for its existence by a sup-
position like the above, the black gaps would remain
unexplained, unless one could make a further draft
on the imagination and suggest that the stars had been
thrown into a vast eddy, or system of eddies, whose
vortices appear as dark holes. Only a maelstrom-
like motion could keep such a funnel open, for with-
out regard to the impulse derived from the projectile,
the proper motions of the stars themselves would
tend to fill it. Perhaps some other cause of the
whirling motion may be found. As we shall see
when we come to the spiral nebulae, gyratory move-
ments are exceedingly prevalent throughout the
universe, and the structure of the Milky Way is every-
where suggestive of them. But this is hazardous
sport even for the imagination — to play with suns as
if they were but thistle-down in the wind or corks in
a mill-race.

9

CURIOSITIES OF THE SKY

Another question arises: What is the thickness of
the hedge of stars through which the holes penetrate ?
Is the depth of the openings proportionate to their
width ? In other words, is the Milky Way round in
section like a rope, or flat and thin like a ribbon?
The answer is not obvious, for we have little or no
information concerning the relative distances of the
faint galactic stars. It would be easier, certainly, to
conceive of openings in a thin belt than in a massive
ring, for in the first case they would resemble mere rifts
and breaks, while in the second they would be like wells
or bore-holes. Then, too, the fact that the Milky Way
is not a continuous body but is made up of stars whose
actual distances apart is great, offers another quan-
dary; persistent and sharply bordered apertures in
such an assemblage are a priori as improbable, if not
impossible, as straight, narrow holes running through
a swarm of bees.

The difficulty of these questions indicates one of
the reasons why it has been suggested that the seem-
ing gaps, or many of them, are not openings at all,
but opaque screens cutting off the light from stars
behind them. That this is quite possible in some cases
is shown by Barnard's later photographs, particularly
those of the singular region around the star Rho
Ophiuchi. Here are to be seen sombre lanes and
patches, apparently forming a connected system
which covers an immense space, and which their dis-
coverer thinks may constitute a "dark nebula." This
seems at first a startling suggestion; but, after all,
why should there not be dark nebulae as well as
visible ones? In truth, it has troubled some as-

10

WINDOWS OF ABSOLUTE NIGHT

tronomers to explain the luminosity of the bright
nebulae, since it is not to be supposed that matter in
so diffuse a state can be incandescent through heat,
and phosphorescent light is in itself a mystery. The
supposition is also in accord with what we know of
the existence of dark solid bodies in space. Many
bright stars are accompanied by obscure companions,
sometimes as massive as themselves; the planets are
non-luminous; the same is true of meteors before
they plunge into the atmosphere and become heated
by friction; and many plausible reasons have been
found for believing that space contains as many ob-
scure as shining bodies of great size. It is not so
difficult, after all, then, to believe that there are im-
mense collections of shadowy gases, and meteoric dust
whose presence is only manifested when they inter-
cept the light coming from shining bodies behind
them.

This would account for the apparent extinguish-
ment of light in open space, which is indicated by the
falling off in relative number of telescopic stars below
the tenth magnitude. Even as things are, the amount
of light coming to us from stars too faint to be seen
with the naked eye is so great that the statement of
it generally surprises persons who are unfamiliar
with the inner facts of astronomy. It has been cal-
culated that on a clear night the total starlight from
the entire celestial sphere amounts to one-sixtieth of
the light of the full moon; but of this less than one-
twenty-fifth is due to stars separately distinguished
by the eye. If there were no obscuring medium in
space, it is probable that the amount of starlight

ii

CURIOSITIES OF THE SKY

would be noticeably and perhaps enormously in-
creased.

But while it seems certain that some of the obscure
spots in the Milky Way are due to the presence of
''dark nebulae, " or concealing veils of one kind or
another, it is equally certain that there are many
which are true apertures, however they may have
been formed, and by whatever forces they may be
maintained. These, then, are veritable windows of
the Galaxy, and when looking out of them one is
face to face with the great mystery of infinite space.
There the known universe visibly ends, but mani-
festly space itself does not end there. It is not within
the power of thought to conceive an end to space,
for the instant we think of a terminal point or line the
mind leaps forward to the beyond. There must be
space outside as well as inside. Eternity of time and
infinity of space are ideas that the intellect cannot
fully grasp, but neither can it grasp the idea of a
limitation to either space or time. The metaphysical
conceptions of hypergeometry, or fourth-dimensional
space, do not aid us.

Having, then, discovered that the universe is a thing
contained in something indefinitely greater than itself ;
having looked out of its windows and found only the
gloom of starless night outside — what conclusions are
we to draw concerning the beyond? It seems as
empty as a vacuum, but is it really so ? If it be, then
our universe is a single atom astray in the infinite;
it is the only island in an ocean without shores; it
is the one oasis in an illimitable desert. Then the
Milky Way, with its wide-flung garland of stars, is

12

WINDOWS OF ABSOLUTE NIGHT

afloat like a tiny smoke-wreath amid a horror of
immeasurable vacancy, or it is an evanescent and
solitary ring of sparkling froth cast up for a moment
on the viewless billows of immensity. From such
conclusions the mind instinctively shrinks. It pre-
fers to think that there is something beyond, though
we cannot see it. Even the universe could not bear
to be alone — a Crusoe lost in the Cosmos! As the
inhabitants of the most elegant chateau, with its
gardens, parks, and crowds of attendants, would die
of loneliness if they did not know that they have
neighbors, though not seen, and that a living world
of indefinite extent surrounds them, so we, when we
perceive that the universe has limits, wish to feel that
it is not solitary; that beyond the hedges and the
hills there are other centres of life and activity.
Could anything be more terrible than the thought of
an isolated universe? The greater the being, the
greater the aversion to seclusion. Only the infinite
satisfies ; in that alone the mind finds rest.

We are driven, then, to believe that the universal
night which envelops us is not tenantlessi that as
we stare out of the star-framed windows of the
Galaxy and see nothing but uniform blackness, the
fault is with our eyes or is due to an obscuring me-
dium. Since our universe is limited in extent, there
must be other universes beyond it on all sides. Per-
haps if we could carry our telescopes to the verge of
the great " Coal-sack" near the "Cross," being then
on the frontier of our starry system, we could discern,
sparkling afar off in the vast night, some of the outer
galaxies. They may be grander than ours, just as

13

CURIOSITIES OF THE SKY

many of the suns surrounding us are immensely
greater than ours. If we could take our stand some-
where in the midst of immensity and, with vision of
infinite reach, look about us, we should perhaps see a
countless number of stellar systems, amid which ours
would be unnoticeable, like a single star among the
multitude glittering in the terrestrial sky on a clear
night. Some might be in the form of a wreath, like
our own; some might be globular, like the great star-
clusters in Hercules and Centaurus; some might be
glittering circles, or disks, or rings within rings. If
we could enter them we should probably find a vast
variety of composition, including elements unknown
to terrestrial chemistry ; for while the visible universe
appears to contain few if any substances not existing
on the earth or in the sun, we have no warrant to
assume that others may not exist in infinite space.

And how as to gravitation? We do not know that
gravitation acts beyond the visible universe, but it
is reasonable to suppose that it does. At any rate,
if we let go its sustaining hand we are lost, and can only
wander hopelessly in our speculations, like children
astray. If the empire of gravitation is infinite, then
the various outer systems must have some, though
measured by our standards an imperceptible, attrac-
tive influence upon each other, for gravitation never
lets go its hold, however great the space over which it
is required to act. Just as the stars about us are all
in motion, so the starry systems beyond our sight
may be in motion, and our system as a whole may
be moving in concert with them. If this be so, then
after interminable ages the aspect of the entire system

14

WINDOWS OF ABSOLUTE NIGHT

of systems must change, its various members assuming
new positions with respect to one another. In the
course of time we may even suppose that our universe
will approach relatively close to one of the others;
and then, if men are yet living on the earth, they may
glimpse through the openings which reveal nothing
to us now, the lights of another nearing star system,
like the signals of a strange squadron, bringing them
the assurance (which can be but an inference at
present) that the ocean of space has other argosies
venturing on its limitless expanse.

There remains the question of the luminiferous \
ether by whose agency the waves of light are borne
through space. The ether is as mysterious as gravita-
tion. With regard to either we only infer its exist-
ence from the effects which we ascribe to it. Evident-
ly the ether must extend as far as the most distant
visible stars. But does it continue on indefinitely in
outer space? If it does, then the invisibility of the
other systems must be due to their distance diminish-
ing the quantity of light that comes from them below
the limit of perceptibility, or to the interposition of
absorbing media; if it does not, then the reason why
we cannot see them is owing to the absence of a
means of conveyance for the light- waves, as the lack
of an interplanetary atmosphere prevents us from
hearing the thunder of sun-spots. (It is interesting
to recall that Mr. Edison was once credited with the
intention to construct a gigantic microphone which
should render the roar of sun-spots audible by trans-
forming the electric vibrations into sound-waves.)
On this supposition each starry system would be en-

CURIOSITIES OF THE SKY

veloped in its own globule of ether, and no light could
cross from one to another. But the probability is
that both the ether and gravitation are ubiquitous,
and that all the stellar systems are immersed in the
former like clouds of phosphorescent organisms in
the sea.

So astronomy carries the mind from height to
greater height. Men were long in accepting the
proofs of the relative insignificance of the earth;
they were more quickly convinced of the comparative
littleness of the solar system; and now the evidence
assails their reason that what they had regarded as
the universe is only one mote gleaming in the sun-
beams of Infinity.

II

STAR-CLOUDS, STAR-CLUSTERS, AND STAR-STREAMS

IN the preceding chapter we have seen something
of the strangely complicated structure of the
Galaxy, or Milky Way. We now proceed to study
more comprehensively that garlanded " Pathway of
the Gods."

Judged by the eye alone, the Milky Way is one of
the most delicately beautiful phenomena in the entire
realm of nature — a shimmer of silvery gauze stretched
across the sky ; but studied in the light of its revela-
tions, it is the most stupendous object presented to
human ken. Let us consider, first, its appearance to
ordinary vision. Its apparent position in the sky
shifts according to the season. On a serene, cloudless
summer evening, in the absence of the moon, whose
light obscures it, one sees the Galaxy spanning the
heavens from north to southeast of the zenith like a
phosphorescent arch. In early spring it forms a
similar but, upon the whole, less brilliant arch west of
the zenith. Between spring and summer it lies like
a long, faint twilight band along the northern horizon.
At the beginning of winter it again forms an arch,
this time spanning the sky from east to west, a little
north of the zenith. These are its positions as

17

CURIOSITIES OF THE SKY

viewed from the mean latitude of the United States.
Even the beginner in star-gazing does not have to
watch it throughout the year in order to be convinced
that it is, in reality, a great circle, extending entirely
around the celestial sphere. We appear to be situ-
ated near its centre, but its periphery is evidently far
away in the depths of space.

Although to the casual observer it seems but a
delicate scarf of light, brighter in some places than in
others, but hazy and indefinite at the best, such is
not its appearance to those who study it with care.
They perceive that it is an organic whole, though
marvellously complex in detail. The telescope shows
that it consists of stars too faint and small through
excess of distance to be separately visible. Of the
hundred million suns which some estimates have fixed
as the probable population of the starry universe,
the vast majority (at least thirty to one) are included
in this strange belt of misty light. But they are not
uniformly distributed in it; on the contrary, they
are arrayed in clusters, knots, bunches, clouds, and
streams. The appearance is somewhat as if the
Galaxy consisted of innumerable swarms of silver-
winged bees, more or less intermixed, some massed
together, some crossing the paths of others, but all
governed by a single purpose which leads them to
encircle the region of space in which we are situ-
ated.

From the beginning of the systematic study of the
heavens, the fact has been recognized that the form
of the Milky Way denotes the scheme of the sidereal
system. At first it was thought that the shape of the

18

STAR CLOUDS, CLUSTERS, AND STREAMS

system was that of a vast round disk, flat like a cheese,
and filled with stars, our sun and his relatively few
neighbors being placed near the centre. According
to this view, the galactic belt was an effect of per-
spective ; for when looking in the direction of the plane
of the disk, the eye ranged through an immense ex-
tension of stars which blended into a glimmering blur,
surrounding us like a ring; while when looking out
from the sides of the disk we saw but few stars, and in
those directions the heavens appeared relatively
blank. Finally it was recognized that this theory
did not correspond with the observed appearances,
and it became evident that the Milky Way was not
a mere effect of perspective, but an actual band of
enormously distant stars, forming a circle about the
sphere, the central opening of the ring (containing
many scattered stars) being many times broader than
the width of the ring itself. Our sun is one of the
scattered stars in the central opening.

As already remarked, the ring of the Galaxy is very
irregular, and in places it is partly broken. With
its sinuous outline, its pendant sprays, its graceful
and accordant curves, its bunching of masses, its
occasional interstices, and the manifest order of a
general plan governing the jumble of its details, it
bears a remarkable resemblance to a garland — a fact
which appears the more wonderful when we recall its
composition. That an elm -tree should trace the
lines of beauty with its leafy and pendulous branches
does not surprise us; but we can only gaze with
growing amazement when we behold a hundred
million suns imitating the form of a chaplet! And

CURIOSITIESOF THE SKY

then we have to remember that this form furnishes
the ground-plan of the universe.

As an indication of the extraordinary speculations
to which the mystery of the Milky Way has given rise,
a theory recently (1909) proposed by Prof. George C.
Comstock may be mentioned. Starting with the
data (first) that the number of stars increases as
the Milky Way is approached, and reaches a maxi-
mum in its plane, while on the other hand the number
of nebulae is greatest outside the Milky Way and in-
creases with distance from it, and (second) that the
Milky Way, although a complete ring, is broad and
diffuse on one side through one-half its course — that
half alone containing nebulae — and relatively narrow
and well defined on the opposite side, the author
of this singular speculation avers that these facts can
best be explained by supposing that the invisible
universe consists of two interpenetrating parts, one
of which is a chaos of indefinite extent, strewn with
stars and nebulous dust, and the other a long, broad
but comparatively thin cluster of stars, including the
sun as one of its central members. This flat star-
cluster is conceived to be moving edgewise through
the chaos, and, according to Professor Comstock, it
acts after the manner of a snow-plough sweeping away
the cosmic dust and piling it on either hand above and
below the plane of the moving cluster. It thus forms
a transparent rift, through which we see farther and
command a view of more stars than through the in-
tensified dust-clouds on either hand. This rift is the
Milky Way. The dust thrown aside toward the poles
of the Milky Way is the substance of the nebulae

20

STAR CLOUDS, CLUSTERS, AND STREAMS

which abound there. Ahead, where the front of the
star-plough is clearing the way, the chaos is nearer
at hand, and consequently there the rift subtends a
broader angle, and is filled with primordial dust,
which, having been annexed by the vanguard of the
star-swarm, forms the nebulae seen only in that part
of the Milky Way. But behind, the rift appears
narrow because there we look farther away between
dust-clouds produced ages ago by the front of the
plough, and no scattered dust remains in that part of
the rift.

In quoting an outline of this strikingly original
theory the present writer should not be understood
as assenting to it. That it appears bizarre is not, in
itself, a reason for rejecting it, when we are dealing
with so problematical and enigmatical a subject as the
Milky Way; but the serious objection is that the
theory does not sufficiently accord with the observed
phenomena. There is too much evidence that the
Milky Way is an organic system, however fantastic
its form, to permit the belief that it can only be a
rift in chaotic clouds. As with every organism, we
find that its parts are more or less clearly repeated
in its ensemble. Among all the strange things that
the Milky Way contains there is nothing so extraor-
dinary as itself. Every astronomer must many
times have found himself marvelling at it in those
comparatively rare nights when it shows all its
beauty and all its strangeness. In its great broken
rifts, divisions, and spirals are found the gigantic
prototypes of similar forms in its star-clouds and
clusters. As we have said, it determines the general

CURIOSITIES OF THE SKY

shape of the whole sidereal system. Some of the
brightest stars in the sky appear to hang like jewels
suspended at the ends of tassels dropped from the
Galaxy. Among these pendants are the Pleiades
and the Hyades. Orion, too, the "Mighty Hunter,"
is caught in "a loop of light" thrown out from it.
The majority of the great first-magnitude stars seem
related to it, as if they formed an inner ring inclined
at an angle of some twenty degrees to its plane.
Many of the long curves that set off from it on both
sides are accompanied by corresponding curves of
lucid stars. In a word, it offers every appearance
of structural connection with the entire starry system.
That the universe should have assumed the form of
a wreath is certainly a matter for astonishment ; but
it would have been still more astonishing if it had
been a cube, a rhomboid, or a dodecahedron, for
then we should have had to suppose that something
resembling the forces that shape crystals had acted
upon the stars, and the difficulty of explaining the
universe by the law of gravitation would have been
increased.

From the Milky Way as a whole we pass to the vast
clouds, swarms, and clusters of stars of which it is
made up. It may be, as some astronomers hold,
that most of the galactic stars are much smaller than
the sun, so that their faintness is not due entirely to
the effect of distance. Still, their intrinsic brilliance
attests their solar character, and considering their
remoteness, which has been estimated at not less than
ten thousand to twenty thousand light-years (a light-
year is equal to nearly six thousand million miles)

22

STAR CLOUDS, CLUSTERS, AND STREAMS

their actual masses cannot be extremely small. The
minutest of them are entitled to be regarded as real
suns, and they vary enormously in magnitude. The
effects of their attractions upon one another can only
be inferred from their clustering, because their
relative movements are not apparent on account of
the brevity of the observations that we can make.
But imagine a being for whom a million years would
be but as a flitting moment; to him the Milky Way
would appear in a state of ceaseless agitation — swirl-
ing with "a fury of whirlpool motion."

The cloud-like aspect of large parts of the Galaxy
must always have attracted attention, even from
naked-eye observers, but the true star-clouds were
first satisfactorily represented in Barnard's photo-
graphs. The resemblance to actual clouds is often
startling. Some are close-packed and dense, like
cumuli; some are wispy or mottled, like cirri. The
rifts and modulations, as well as the general outlines,
are the same as those of clouds of vapor or dust, and
one notices also the characteristic thinning out at the
edges. But we must beware of supposing that the
component suns are thickly crowded as the particles
forming an ordinary cloud. They look, indeed, as if
they were matted together, because of the irradiation
of light, but in reality millions and billions of miles
separate each star from its neighbors. Nevertheless
they form real assemblages, whose members are far
more closely related to one another than is our sun
to the stars around him, and if we were in the Milky
Way the aspect of the nocturnal sky would be mar-
vellously different from its present appearance.

CURIOSITIES OF THE SKY

Stellar clouds are characteristic of the Galaxy and
are not found beyond its borders, except in the
"Magellanic Clouds" of the southern hemisphere,
which resemble detached portions of the Milky Way.
These singular objects form as striking a peculiarity of
the austral heavens as does the great "Coal -sack"
described in Chapter I. But it is their isolation that
makes them so remarkable, for their composition is
essentially galactic, and if they were included within
its boundaries they would not appear more wonderful
than many other parts of the Milky Way. Placed
where they are, they look like masses fallen from the
great stellar arch. They are full of nebulae and star-
clusters, and show striking evidences of spiral move-
ment.

Star-swarms, which are also characteristic features
of the Galaxy, differ from star-clouds very much in
the way that their name would imply — i.e., their
component stars are so arranged, even when they are
countless in number, that the idea of an exceedingly
numerous assemblage rather than that of a cloud is
impressed on the observer's mind. In a star-swarm
the separate members are distinguishable because
they are either larger or nearer than the stars com-
posing a "cloud." A splendid example of a true
star-swarm is furnished by Chi Persei, in that part of
the Milky Way which runs between the constella-
tions Perseus and Cassiopeia. This swarm is much
coarser than many others, and can be seen by the
naked eye. In a small telescope it appears double,
as if the suns composing it had divided into two
parties which keep on their way side by side, with

24

STAR CLOUDS, CLUSTERS, AND STREAMS

some commingling of their members where the skirts
of the two companies come in contact.

Smaller than either star-clouds or star-swarms, and
differing from both in their organization, are star-
clusters. These, unlike the others, are found outside
as well as inside the Milky Way, although they are
more numerous inside its boundaries than elsewhere.
The term star-cluster is sometimes applied, though
improperly, to assemblages which are rather groups,
such, for instance, as the Pleiades. In their most
characteristic aspect star-clusters are of a globular
shape — globes of suns! A famous example of a
globular star-cluster, but one not included in the
Milky Way, is the " Great Cluster in Hercules."
This is barely visible to the naked eye, but a small
telescope shows its character, and in a large one it
presents a marvellous spectacle. Photographs of
such clusters are, perhaps, less effective than those of
star-clouds, because the central condensation of stars
in them is so great that their light becomes blended
in an indistinguishable blur. The beautiful effect of
the incessant play of infinitesimal rays over the
apparently compact surface of the cluster, as if it
were a globe of the finest frosted silver shining in an
electric beam, is also lost in a photograph. Still,
even to the eye looking directly at the cluster through
a powerful telescope, the central part of the wonderful
congregation seems almost a solid mass in which the
stars are packed like the ice crystals in a snowball.

The same question rises to the lips of every ob-
server: How can they possibly have been brought
into such a situation? The marvel does not grow

CURIOSITIES OF THE SKY

less when we know that, instead of being closely com-
pacted, the stars of the cluster are probably separated
by millions of miles; for we know that their distances
apart are slight as compared with their remoteness
from the earth. Sir William Herschel estimated
their number to be about fourteen thousand, but in
fact they are uncountable. If we could view them
from a point just within the edge of the assemblage,
they would offer the appearance of a hollow hemi-
sphere emblazoned with stars of astonishing brill-
iancy; the near-by ones unparalleled in splendor by
any celestial object known to us, while the more dis-
tant ones would resemble ordinary stars. An in-
habitant of the cluster would not know, except by a
process of ratiocination, that he was dwelling in a
globular assemblage of suns; only from a point far
outside would their spherical arrangement become
evident to the eye. Imagine fourteen thousand fire-
balloons arranged with an approach to regularity in
a spherical space — say, ten miles in diameter; there
would be an average of less than thirty in every
cubic mile, and it would be necessary to go to a con-
siderable distance in order to see them as a globular
aggregation ; yet from a point sufficiently far away
they would blend into a glowing ball.

Photographs show even better than the best tele-
scopic views that the great cluster is surrounded with
a multitude of dispersed stars, suggestively arrayed
in more or less curving lines, which radiate from the
principal mass, with which their connection is mani-
fest. These stars, situated outside the central sphere,
look somewhat like vagrant bees buzzing round a dense

STAR-CLUSTER IN HERCULES
(Photographed with a two- foot reflector)

STAR CLOUDS, CLUSTERS, AND STREAMS

swarm where the queen bee is settling. Yet while
there is so much to suggest the operation of central
forces, bringing and keeping the members of the
cluster together, the attentive observer is also im-
pressed with the idea that the whole wonderful
phenomenon may be ike result of explosion. As soon
as this thought seizes the mind, confirmation of it
seems to be found in the appearance of the outlying
stars, which could be as readily explained by the
supposition that they have been blown apart as that
they have flocked together toward a centre. The
probable fact that the stars constituting the cluster
are very much smaller than our sun might be regarded
as favoring the hypothesis of an explosion. Of their
real size we know nothing, but, on the basis of an
uncertain estimate of their parallax, it has been cal-
culated that they may average forty-five thousand
miles in diameter — something more than half the
diameter of the planet Jupiter. Assuming the same
mean density, fourteen thousand such stars might
have been formed by the explosion of a body about
twice the size of the sun. This recalls the theory
of Olbers, which has never been altogether abandoned
or disproved, that the Asteroids were formed by the
explosion of a planet circulating between the orbits
of Mars and Jupiter. The Asteroids, whatever their
manner of origin, form a ring around the sun; but,
of course, the explosion of a great independent body,
not originally revolving about a superior centre of
gravitative force, would not result in the formation
of a ring of small bodies, but rather of a dispersed
mass of them. But back of any speculation of this

29

CURIOSITIES OF THE SKY

kind lies the problem, at present insoluble: How
could the explosion be produced ? (See the question
of explosions in Chapters VI and XIV.)

Then, on the other hand, we have the observation
of Herschel, since abundantly confirmed, that space
is unusually vacant in the immediate neighborhood of
condensed star-clusters and nebulae, which, as far as
it goes, might be taken as an indication that the
assembled stars had been drawn together by their
mutual attractions, and that the tendency to aggre-
gation is still bringing new members toward the
cluster. But in that case there must have been
an original condensation of stars at that point in
space. This could probably have been produced by
the coagulation of a great nebula into stellar nuclei,
a process which seems now to be taking place in the
Orion Nebula.

A yet more remarkable globular star-cluster exists
in the southern hemisphere, Omega Centauri. In
this case the central condensation of stars presents
an almost uniform blaze of light. Like the Hercules
cluster, that in Centaurus is surrounded with stars
scattered over a broad field and showing an appear-
ance of radial arrangement. In fact, except for its
greater richness, Omega Centauri is an exact duplicate
of its northern rival. Each appears to an imaginative
spectator as a veritable ''city of suns." Mathe-
matics shrinks from the task of disentangling the
maze of motions in such an assemblage. It would seem
that the chance of collisions is not to be neglected,
and this idea finds a certain degree of confirmation
in the appearance of " temporary stars" which have

30

GREAT SOUTHERN STAR-CLUSTER, OMEGA CENTAURI

STAR CLOUDS, CLUSTERS, AND STREAMS

more than once blazed out in, or close by, globular
star-clusters.

This leads up to the notable fact, first established
by Professor Bailey a few years ago, that such clusters
are populous with variable stars. Omega Centauri
and the Hercules cluster are especially remarkable in
this respect. The variables found in them are all
of short period and the changes of light show a note-
worthy tendency to uniformity. The first thought
is that these phenomena must be due to collisions
among the crowded stars, but, if so, the encounters
cannot be between the stars themselves, but probably
between stars and meteor swarms revolving around
them. Such periodic collisions might go on for ages
without the meteors being exhausted by incorpora-
tion with the stars. This explanation appears all
the more probable because one would naturally ex-
pect that flocks of meteors would abound in a close
aggregation of stars. It is also consistent with
Perrine's discovery — that the globular star-clusters
are powdered with minute stars strewn thickly among
the brighter ones.

In speaking of Professor Comstock's extraordinary
theory of the Milky Way, the fact was mentioned that,
broadly speaking, the nebulas are less numerous in
the galactic belt than in the comparatively open
spaces on either side of it, but that they are, neverthe-
less, abundant in the broader half of the Milky Way
which he designates as the front of the gigantic
"plough" supposed to be forcing its way through
the enveloping chaos. In and around the Sagit-
tarius region the intermingling of nebulae and

33

CURIOSITIES OF THE SKY

galactic star clouds and clusters is particularly re-
markable. That there is a causal connection no
thoughtful observer can doubt. We are unable to
get away from the evidence that a nebula is like a
seed-ground from which stars spring forth; or we
may say that nebulas resemble clouds in whose
bosom raindrops are forming. The wonderful as-
pect of the admixtures of nebulae and star-clusters
in Sagittarius has been described in Chapter I. We
now come to a still more extraordinary phenomenon
of this kind — the Pleiades nebulas.

The group of the Pleiades, although lying outside
the main course of the Galaxy, is connected with it
by a faint loop, and is the scene of the most remark-
able association of stars and nebulous matter known
in the visible universe. The naked eye is unaware
of the existence of nebulas in the Pleiades, or, at the
best, merely suspects that there is something of the
kind there; and even the most powerful telescopes
are far from revealing the full wonder of the spectacle ;
but in photographs which have been exposed for
many hours consecutively, in order to accumulate the
impression of the actinic rays, the revelation is stun-
ning. The principal stars are seen surrounded by,
and, as it were, drowned in, dense nebulous clouds of
an unparalleled kind. The forms assumed by these
clouds seem at first sight inexplicable. They look
like fleeces, or perhaps more like splashes and daubs
of luminous paint dashed carelessly from a brush.
But closer inspection shows that they are, to a large
extent, woven out of innumerable threads of filmy
texture, and there are many indications of spiral

34

STAR CLOUDS, CLUSTERS, AND STREAMS

tendencies. Each of the bright stars of the group —
Alcyone, Merope, Maia, Electra, Taygeta, Atlas — is
the focus of a dense fog (totally invisible, remember,
alike to the naked eye and to the telescope), and these
particular stars are veiled from sight behind the
strange mists. Running in all directions across the
relatively open spaces are nebulous wisps and streaks
of the most curious forms. On some of the nebular
lines, which are either straight throughout, or if they
change direction do so at an angle, little stars are
strung like beads. In one case seven or eight stars
are thus aligned, and, as if to emphasize their depend-
ence upon the chain which connects them, when it
makes a slight bend the file of stars turns the same
way. Many other star rows in the group suggest by
their arrangement that they, too, were once strung
upon similar threads which have now disappeared,
leaving the stars spaced along their ancient tracks.
We seem forced to the conclusion that there was a
time when the Pleiades were embedded in a vast
nebula resembling that of Orion, and that the cloud
has now become so rare by gradual condensation
into stars that the merest trace of it remains, and this
would probably have escaped detection but for the
remarkable actinic power of the radiant matter of
which it consists. The richness of many of these
faint nebulous masses in ultra-violet radiations,
which are those that specially affect the photographic
plate, is the cause of the marvellous revelatory power
of celestial photography. So the veritable unseen
universe, as distinguished from the "unseen universe"
of metaphysical speculation, is shown to us.

37

CURIOSITIES OF THE SKY

A different kind of association between stars and
nebulae is shown in some surprising photographic
objects in the constellation Cygnus, where long, wispy
nebulae, billions of miles in length, some of them
looking like tresses streaming in a breeze, lie amid
fields of stars which seem related to them. But the
relation is of a most singular kind, for notwithstand-
ing the delicate structure of the long nebulae they ap-
pear to act as barriers, causing the stars to heap
themselves on one side. The stars are two, three, or
four times as numerous on one side of the nebulae as
on the other. These nebulae, as far as appearance
goes, might be likened to rail fences, or thin hedges,
against which the wind is driving drifts of powdery
snow, which, while scattered plentifully all around,
tends to bank itself on the leeward side of the ob-
struction. The imagination is at a loss to account
for these extraordinary phenomena; yet there they
are, faithfully giving us their images whenever the
photographic plate is exposed to their radiations.

Thus the more we see of the universe with improved
methods of observation, and the more we invent aids
to human senses, each enabling us to penetrate a
little deeper into the unseen, the greater becomes the
mystery. The telescope carried us far, photography
is carrying us still farther; but what as yet unimagined
instrument will take us to the bottom, the top, and
the end ? And then, what hitherto untried power of
thought will enable us to comprehend the meaning of
it all?

Ill

STELLAR MIGRATIONS

TO the untrained eye the stars and the planets are
not distinguishable. It is customary to call
them all alike ' 'stars/' But since the planets more
or less rapidly change their places in the sky, in
consequence of their revolution about the sun, while
the stars proper seem to remain always in the same
relative positions, the latter are spoken of as "fixed
stars." In the beginnings of astronomy it was not
known that the "fixed stars" had any motion in-
dependent of their apparent annual revolution with
the whole sky about the earth as a seeming centre.
Now, however, we know that the term "fixed stars"
is paradoxical, for there is not a single really fixed
object in the whole celestial sphere. The apparent
fixity in the positions of the stars is due to their im-
mense distance, combined with the shortness of the
time during which we are able to observe them. It
is like viewing the plume of smoke issuing from a
steamer, hull down, at sea : if one does not continue to
watch it for a long time it appears to be motionless,
although in reality it may be travelling at great speed
across the line of sight. Even the planets seem fixed
in position if one watches them for a single night only,
3 39

CURIOSITIES OF THE SKY

and the more distant ones do not sensibly change their
places, except after many nights of observation.
Neptune, for instance, moves but little more than
two degrees in the course of an entire year, and in a
month its change of place is only about one-third of
the diameter of the full moon.

Yet, fixed as they seem, the stars are actually
moving with a speed in comparison with which, in
some cases, the planets might almost be said to stand
fast in their tracks. Jupiter's speed in his orbit is
about eight miles per second, Neptune's is less than
three and one-half miles, and the earth's is about
eighteen and one-half miles; while there are "fixed
stars" which move two hundred or three hundred
miles per second. They do not all, however, move
with so great a velocity, for some appear to travel
no faster than the planets. But in all cases, notwith-
standing their real speed, long-continued and exceed-
ingly careful observations are required to demonstrate
that they are moving at all. No more overwhelming
impression of the frightful depths of space in which
the stars are buried can be obtained than by reflect-
ing upon the fact that a star whose actual motion
across the line of sight amounts to two hundred miles
per second does not change its apparent place in the
sky, in the course of a thousand years, sufficiently to
be noticed by the casual observer of the heavens!

There is one vast difference between the motions
of the stars and those of the planets to which atten-
tion should at once be called: the planets, being under
the control of a central force emanating from their
immediate master, the sun, all move in the same

40

STELLAR MIGRATIONS

direction and in orbits concentric about the sunj
the stars, on the other hand, move in every conceivable
direction and have no apparent centre of motion, for
all efforts to discover such a centre have failed. At
one time, when theology had finally to accept the
facts of science, a grandiose conception arose in some
pious minds, according to which the Throne of God
was situated at the exact centre of His Creation, and,
seated there, He watched the magnificent spectacle
of the starry systems obediently revolving around
Him. Astronomical discoveries and speculations
seemed for a time to afford some warrant for this
view, which was, moreover, an acceptable substitute
for the abandoned geocentric theory in minds that
could only conceive of God as a superhuman artificer,
constantly admiring His own work. No longer ago
than the middle of the nineteenth century a German
astronomer, Maedler, believed that he had actually
found the location . of the centre about which the
stellar universe revolved. He placed it in the group
of the Pleiades, and upon his authority an extraor-
dinary imaginative picture was sometimes drawn of
the star Alcyone, the brightest of the Pleiades, as
the very seat of the Almighty. This idea even seemed
to gain a kind of traditional support from the mystic
significance, without known historical origin, which
has for many ages, and among widely separated
peoples, been attached to the remarkable group of
which Alcyone is the chief. But since Maedler's i
time it has been demonstrated that the Pleiades
cannot be the centre of revolution of the universe,
and, as already remarked, all attempts to find or fix

41

CURIOSITIES OF THE SKY

such a centre have proved abortive. Yet so powerful
was the hold that the theory took upon the popular
imagination, that even to-day astronomers are often
asked if Alcyone is not the probable site of "Jerusalem
the Golden."

If there were a discoverable centre of predominant
gravitative power, to which the motions of all the
stars could be referred, those motions would ap-
pear less mysterious, and we should then be able
to conclude that the universe was, as a whole, a proto-
type of the subsidiary systems of which it is com-
posed. We should look simply to the law of gravita-
tion for an explanation, and, naturally, the centre
would be placed within the opening enclosed by the
Milky Way. If it were there the Milky Way itself
should exhibit signs of revolution about it, like a
wheel turning upon its hub. No theory of the star
motions as a whole could stand which failed to take
account of the Milky Way as the basis of all. But
the very form of that divided wreath of stars forbids
the assumption of its revolution around a centre.
Even if it could be conceived as a wheel having no
material centre it would not have the form which it
actually presents. As was shown in Chapter II, there
is abundant evidence of motion in the Milky Way;
but it is not motion of the system as a whole, but
motion affecting its separate parts. Instead of all
moving one way, the galactic stars, as far as their
movements can be inferred, are governed by local
influences and conditions. They appear to travel
crosswise and in contrary directions, and perhaps
they eddy around foci where great numbers have

42

STELLAR MIGRATIONS

assembled; but of a universal revolution involving
the entire mass we have no evidence.

Most of our knowledge of star motions, called " prop-
er motions," relates to individual stars and to a few
groups which happen to be so near that the effects
of their movements are measurable. In some cases
the motion is so rapid (not in appearance, but in
reality) that the chief difficulty is to imagine how it
can have been imparted, and what will eventually
become of the "runaways." Without a collision,
or a series of very close approaches to great gravita-
tive centres, a star travelling through space at the
rate of two hundred or three hundred miles per second
could not be arrested or turned into an orbit which
would keep it forever flying within the limits of the
visible universe. A famous example of these speed-
ing stars is "1830 Groombridge," a star of only the
sixth magnitude, and consequently just visible to the
naked eye, whose motion across the line of sight is so
rapid that it moves upon the face of the sky a distance
equal to the apparent diameter of the moon every
280 years. The distance of this star is at least
200,000,000,000,000 miles, and may be two or three
times greater, so that its actual speed cannot be less
than two hundred, and may be as much as four hun-
dred, miles per second. It could be turned into a new
course by a close approach to a great sun, but it
could only be stopped by collision, head-on, with a
body of enormous mass. Barring such accidents it
must, as far as we can see, keep on until it has traversed
our stellar system, whence it may escape and pass out
into space beyond, to join, perhaps, one of those

43

CURIOSITIES OF THE SKY

other universes of which we have spoken. Arcturus,
one of the greatest suns in the universe, is also a run-
away, whose speed of flight has been estimated all the
way from fifty to two hundred miles per second.
Arcturus, we have every reason to believe, possesses
hundreds of times the mass of our sun — think, then,
of the prodigious momentum that its motion implies !
Sirius moves more moderately, its motion across the
line of sight amounting to only ten miles per second,
but it is at the same time approaching the sun at
about the same speed, its actual velocity in space
being the resultant of the two displacements.

What has just been said about the motion of Sirius
brings us to another aspect of this subject. The
fact is, that in every case of stellar motion the dis-
placement that we observe represents only a part of
the actual movement of the star concerned. There
are stars whose motion carries them straight toward
or straight away from the earth, and such stars, of
course, show no cross motion. But the vast majority
are travelling in paths inclined from a perpendicular
to our line of sight. Taken as a whole, the stars may
be said to be flying about like the molecules in a mass
1 of gas. The discovery of the radial component in the
movements of the stars is due to the spectroscope.
J If a star is approaching, its spectral lines are shifted
\ toward the violet end of the spectrum by an amount
, depending upon the velocity of approach ; if it is
; receding, the lines are correspondingly shifted toward
! the red end. Spectroscopic observation, then, com-
bined with micrometric measurement of the cross
motion, enables us to detect the real movement of

44

STELLAR MIGRATIONS

the star in space. Sometimes it happens that a
star's radial movement is periodically reversed; first
it approaches, and then it recedes. This indicates
that it is revolving around a near-by companion, which
is often invisible, and superposed upon this motion is
that of the two stars concerned, which together may
be approaching or receding or travelling across the
line of sight. Thus the complications involved in the
stellar motions are often exceedingly great and
puzzling.

Yet another source of complication exists in the
movement of our own star, the sun. There is no
more difficult problem in astronomy than that of
disentangling the effects of the solar motion from
those of the motions of the other stars. But the
problem, difficult as it is, has been solved, and upon its
solution depends our knowledge of the speed and
direction of the movement of the solar system
through space, for of course the sun carries its planets
with it. One element of the solution is found in the
fact that, as a result of perspective, the stars toward
which we are going appear to move apart toward all
points of the compass, while those behind appear to
close up together. Then the spectroscopic principle
already mentioned is invoked for studying the shift
of the lines, which is toward the violet in the stars
ahead of us and toward the red in those that we are
leaving behind. Of course the effects of the independ-
ent motions of the stars must be carefully excluded.
The result of the studies devoted to this subject is to
show that we are travelling at a speed of twelve to
fifteen miles per second in a northerly direction,

45

CURIOSITIES OF THE SKY

toward the border of the constellations Hercules and
Lyra. A curious fact is that the more recent esti-
mates show that the direction is not very much out
of a straight line drawn from the sun to the star
Vega, one of the most magnificent suns in the heavens.
But it should not be inferred from this that Vega
is drawing us on; it is too distant for its gravitation to
have such an effect.

Many unaccustomed thoughts are suggested by
this mighty voyage of the solar system. Whence
have we come, and whither do we go ? Every year
of our lives we advance at least 375,000,000 miles.
Since the traditional time of Adam the sun has led
his planets through the wastes of space no less than
225,000,000,000 miles, or more than 2400 times the
distance that separates him from the earth. Go
back in imagination to the geologic ages, and try to
comprehend the distance over which the earth has
flown. Where was our little planet when it emerged
out of the clouds of chaos ? Where was the sun when
his "thunder march" began? What strange con-
stellations shone down upon our globe when its
masters of life were the monstrous beasts of the
"Age of Reptiles?" A million years is not much of
a span of time in geologic reckoning, yet a million
years ago the earth was farther from its present place
in space than any of the stars with a measurable
parallax are now. It was more than seven times as
far as Sirius, nearly fourteen times as far as Alpha
Centauri, three times as far as Vega, and twice as far
as Arcturus. But some geologists demand two
hundred, three hundred, even one thousand million

46

STELLAR MIGRATIONS

years to enable them to account for the evolutionary
development of the earth and its inhabitants. In a
thousand million years the earth would have travelled
farther than from the remotest conceivable depths
of the Milky Way!

Other curious reflections arise when we think of
the form of the earth's track as it follows the lead
of the sun, in a journey which has neither known be-
ginning nor conceivable end. There are probably
many minds which have found a kind of consolation
in the thought that every year the globe returns to the
same place, on the same side of the sun. This idea
may have an occult connection with our traditional
regard for anniversaries. When that period of the
year returns at which any great event in our lives
has occurred we have the feeling that the earth, in its
annual round, has, in a manner, brought us back to
the scene of that event. We think of the earth's
orbit as a well-worn path which we traverse many
times in the course of a lifetime. It seems familiar
to us, and we grow to have a sort of attachment to it.
The sun we are accustomed to regard as a fixed centre
in space, like the mill or pump around which the
harnessed patient mule makes his endless circuits.
But the real fact is that the earth never returns to the
place in space which it has once quitted. In con-
sequence of the motion of the sun carrying the earth
and the other planets along, the track pursued by our
globe is a vast spiral in space continually developing
and never returning upon its course. It is probable
that the tracks of the sun and the other stars are also
irregular, and possibly spiral, although, as far as can

47

CURIOSITIES OF THE SKY

be at present determined, they appear to be prac-
tically straight. Every star, wherever it may be
situated, is attracted by its fellow-stars from many
sides at once, and although the force is minimized by
distance, yet in the course of many ages its effects
must become manifest.

Looked at from another side, is there not something
immensely stimulating and pleasing to the imagina-
tion in the idea of so stupendous a journey, which
makes all of us the greatest of travellers? In the
course of a long life a man is transported through
space thirty thousand million miles; Halley's Comet
does not travel one-quarter as far in making one of its
immense circuits. And there are adventures on this
voyage of which we are just beginning to learn to
take account. Space is full of strange things, and the
earth must encounter some of them as it advances
through the unknown. Many singular speculations
have been indulged in by astronomers concerning the
possible effects upon the earth of the varying state of
the space that it traverses. Even the alternation of
hot and glacial periods has sometimes been ascribed to
this source. When tropical life flourished around
the poles, as the remains in the rocks assure us, the
needed high temperature may, it has been thought,
have been derived from the presence of the earth in a
warm region of space. Then, too, there is a certain
interest for us in the thought of what our familiar
planet has passed through. We cannot but admire
it for its long journeying as we admire the traveller
who comes to us from remote and unexplored lands,
or as we gaze with a glow of interest upon the first

48

STELLAR MIGRATIONS

locomotive that has crossed a continent, or a ship
that has visited the Arctic or Antarctic regions. If
we may trust the indications of its present course,
the earth, piloted by the sun, has come from the
Milky Way in the far south and may eventually rejoin
that mighty band of stars in the far north.

While the stars in general appear to travel inde-
pendently of one another, except when they are
combined in binary or trinary systems, there are
notable exceptions to this rule. In some quarters of
the sky we behold veritable migrations of entire
groups of stars whose members are too widely sepa-
rated to show ' any indications of revolution about a
common centre of gravity. This leads us back again
to the wonderful group of the Pleiades. All of the
principal stars composing that group are travelling in
virtually parallel lines. Whatever force set them
going evidently acted upon all alike. This might be
explained by the assumption that when the original
projective force acted upon them they were more
closely united than they are at present, and that in
drifting apart they have not lost the impulse of the
primal motion. Or it may be supposed that they are
carried along by some current in space, although it
would be exceeding difficult, in the present state of
our knowledge, to explain the nature of such a current.
Yet the theory of a current has been proposed. As
to an attractive centre around which they might
revolve, none has been found. Another instance of
similar "star-drift" is furnished by five of the seven
stars constituting the figure of the "Great Dipper."
In this case the stars concerned are separated very

49

CURIOSITIES OF THE SKY

widely, the two extreme ones by not less than fifteen
degrees, so that the idea of a common motion would
never have been suggested by their aspect in the sky;
and the case becomes the more remarkable from the
fact that among and between them there are other
stars, some of the same magnitude, which do not share
their motion, but are travelling in other directions.
Still other examples of the same phenomenon are
found in other parts of the sky. Of course, in the case
of compact star-clusters, it is assumed that all the
members share a like motion of translation through
space, and the same is probably true of dense star-
swarms and star-clouds.

The whole question of star-drift has lately assumed
a new phase, inconsequence of the investigations of
Kapteyn, Dyson, and Eddington on the "systematic
motions of the stars." This research will, it is hoped,
lead to an understanding of the general law governing
the movements of the whole body of stars constituting
the visible universe. Taking about eleven hundred
stars whose proper motions have been ascertained
with an approach to certainty, and which are dis-
tributed in all parts of the sky, it has been shown
that there exists an apparent double drift, in two in-
dependent streams, moving in different and nearly
opposed directions. The apex of the motion of what
is called "Stream I " is situated, according to Professor
Kapteyn, in right ascension 85°, declination south
11°, which places it just south of the constellation
Orion; while the apex of "Stream II" is in right
ascension 260°, declination south 48°, placing it in
the constellation Ara, south of Scorpio. The two

5°

STELLAR MIGRATIONS

apices differ very nearly 180° in right ascension and
about 120° in declination. The discovery of these
vast star-streams, if they really exist, is one of the
most extraordinary in modern astronomy. It offers
the correlation of stellar movements needed as the
basis of a theory of those movements, but it seems
far from revealing a physical cause for them. As
projected against the celestial sphere the stars form-
ing the two opposite streams appear intermingled,
some obeying one tendency and some the other. As
Professor Dyson has said, the hypothesis of this double
movement is of a revolutionary character, and calls
for further investigation. Indeed, it seems at first
glance not less surprising than would be the observa-
tion that in a snow-storm the flakes over our heads
were divided into two parties and driving across each
other's course in nearly opposite directions, as if
urged by interpenetrating winds.

But whatever explanation may eventually be found
for the motions of the stars, the knowledge of the
existence of those motions must always afford a new
charm to the contemplative observer of the heavens,
for they impart a sense of life to the starry system
that would otherwise be lacking. A stagnant universe,
with every star fixed immovably in its place, would
not content the imagination or satisfy our longing
for ceaseless activity. The majestic grandeur of the
evolutions of the celestial hosts, the inconceivable
vastness of the fields of space in which they are
executed, the countless numbers, the immeasurable
distances, the involved convolutions, the flocking
and the scattering, the interpenetrating marches and

CURIOSITIES OF THE SKY

countermarches, the strange community of impulsion
affecting stars that are wide apart in space and caus-
ing them to traverse the general movement about
them like aides and despatch-bearers on a battle-
field— all these arouse an intensity of interest which is
heightened by the mystery behind them.

IV

THE PASSING OF THE CONSTELLATIONS

FROM a historical and picturesque point of view,
one of the most striking results of the motions
of the stars described in the last chapter is their effect
upon the forms of the constellations, which have been
watched and admired by mankind from a period so
early that the date of their invention is now unknown.
The constellations are formed by chance combina-
tions of conspicious stars, like figures in a kaleidoscope,
and if our lives were commensurate with the aeons of
cosmic existence we should perceive that the kaleido-
scope of the heavens was ceaselessly turning and throw-
ing the stars into new symmetries. Even if the stars
stood fast, the motion of the solar system would
gradually alter the configurations, as the elements of
a landscape dissolve and recombine in fresh group-
ings with the traveller's progress amid them. But
with the stars themselves all in motion at various
speeds and in many directions, the changes occur more
rapidly. Of course, "rapid" is here to be understood
in a relative sense ; the wheel of human history to an
eye accustomed to the majestic progression of the
universe would appear to revolve with the velocity
of a whirling dynamo. Only the deliberation of geo-

53

CURIOSITIES OF THE SKY

logical movements can be contrasted with the evolu-
tion and devolution of the constellations.

And yet this secular fluctuation of the constellation
figures is not without keen interest for the meditative
observer. It is another reminder of the swift muta-
bility of terrestrial affairs. To the passing glance,
which is all that we can bestow upon these figures, they
appear so immutable that they have been called into
service to form the most lasting records of ancient
thought and imagination that we possess. In the
forms of the constellations, the most beautiful, and, in
imaginative quality, the finest, mythology that the
world has ever known has been perpetuated. Yet, in
a broad sense, this scroll of human thought imprinted
on the heavens is as evanescent as the summer clouds.
Although more enduring than parchment, tombs,
pyramids, and temples, it is as far as they from truly
eternizing the memory of what man has fancied and
done.

Before studying the effects that the motions of the
stars have had and will have upon the constellations,
it is worth while to consider a little further the im-
portance of the stellar pictures as archives of history.
To emphasize the importance of these effects it is only
necessary to recall that the constellations register
the oldest traditions of our race. In the history of
primeval religions they are the most valuable of docu-
ments. Leaving out of account for the moment the
more familiar mythology of the Greeks, based on
something older yet, we may refer for illustration to
that of the mysterious Maya race of America. At
Izamal, in Yucatan, says Mr. Stansbury Hagar, is

54

PASSING OF THE CONSTELLATIONS

a group of ruins perched, after the Mexican and
Central- American plan, on the summits of pyramidal
mounds which mark the site of an ancient theogonic
centre of the Mayas. Here the temples all evi-
dently refer to a cult based upon the constellations as
symbols. The figures and the names, of course, were
not the same as those that we have derived from our
Aryan ancestors, but the star groups were the same
or nearly so. For instance, the loftiest of the temples
at Izamal was connected with the sign of the con-
stellation known to us as Cancer, marking the place
of the sun at the summer solstice, at which period the
sun was supposed to descend at noon like a great bird
of fire and consume the offerings left upon the altar.
Our Scorpio was known to the Mayas as the sign of
the "Death God." Our Libra, the "Balance," with
which the idea of a divine weighing out of justice has
always been connected, seems to be identical with the
Mayan constellation Teoyaotlatohua with which was
associated a temple where dwelt the priests whose
special business it was to administer justice and to
foretell the future by means of information obtained
from the spirits of the dead. Orion, the "Hunter"
of our celestial mythology, was among the Mayas a
"Warrior," while Sagittarius and others of our con-
stellations were known to them (under different names,
of course), and all were endowed with a religious
symbolism. And the same star figures, having the
same significance, were familiar to the Peruvians, as
shown by the temples at Cuzco. Thus the imagina-
tion of ancient America sought in the constellations
symbols of the unchanging gods.
* 55

CURIOSITIES OF THE SKY

But, in fact, there is no nation and no people that
has not recognized the constellations, and at one
period or another in its history employed them in
some symbolic or representative capacity. As han-
dled by the Greeks from prehistoric times, the con-
stellation myths became the very soul of poetry. The
imagination of that wonderful race idealized the
principal star groups so effectively that the figures
and traditions thus attached to them have, for civil-
ized mankind, displaced all others, just as Greek art
in its highest forms stands without parallel and
eclipses every rival. The Romans translated no
heroes and heroines of the mythical period of their
history to the sky, and the deified Ca3sars never en-
tered that lofty company, but the heavens are filled
with the early myths of the Greeks. Herakles nightly
resumes his mighty labors in the stars; Zeus, in the
form of the white "Bull," Taurus, bears the fair
Europa on his back through the celestial waves;
Andromeda stretches forth her shackled arms in the
star-gemmed ether, beseeching aid ; and Perseus, in a
blaze of diamond armor, revives his heroic deeds amid
sparkling clouds of stellar dust. There, too, sits Queen
Cassiopeia in her dazzling chair, while the Great
King, Cepheus, towers gigantic over the pole. Pro-
fessor Young has significantly remarked that a great
number of the constellations are connected in some
way or other with the Argonautic Expedition — that
strangely fascinating legend of earliest Greek story
which has never lost its charm for mankind. In view
of all this, we may well congratulate ourselves that the
constellations will outlast our time and the time of

56

PASSING OF THE CONSTELLATIONS

countless generations to follow us; and yet they are
very far from being eternal. Let us now study some
of the effects of the stellar motions upon them.

We begin with the familiar figure of the "Great
Dipper." He who has not drunk inspiration from
its celestial bowl is not yet admitted to the circle of
Olympus. This figure is made up of seven con-
spicuous stars in the constellation Ursa Major, the
" Greater Bear." The handle of the "Dipper" cor-
responds to the tail of the imaginary "Bear," and the
bowl lies upon his flank. In fact, the figure of a dipper
is so evident and that of a bear so unevident, that to
most persons the "Great Dipper" is the only part of
the constellation that is recognizable. Of the seven
stars mentioned, six are of nearly equal brightness,
ranking as of the second magnitude, while the seventh
is of only the third magnitude. The difference is very
striking, since every increase of one magnitude in-
volves an increase of two-and-a-half times in bright-
ness. There appears to be little doubt that the faint
star, which is situated at the junction of the bowl
and the handle, is a variable of long period, since
three hundred years ago it was as bright as its com-
panions. But however that may be, its relative faint-
ness at the present time interferes but little with the
perfection of the "Dipper's" figure. In order the
more readily to understand the changes wrhich are
taking place, it will be well to mention both the names
and the Greek letters which are attached to the seven
stars. Beginning at the star in the upper outer edge
of the rim of the bowl and running in regular order
round the bottom and then out to the end of the handle,

57

CURIOSITIES OF THE SKY

the names and letters are as follows: Dubhe (a),
Merak (j3), Phaed (7), Megrez (8), Alioth (e),
Mizar (c), and Benetnasch (ij). Megrez is the faint
star already mentioned at the junction of the bowl
and handle, and Mizar, in the middle of the handle, has
a close, naked-eye companion which is named Alcor.

THE "GREAT DIPPER" AS IT IS

AS IT WILL BE

AS IT WAS FORMERLY

58

PASSING OF THE CONSTELLATIONS

The Arabs called this singular pair of stars ''The
Horse and Rider." Merak and Dubhe are called
4 'The Pointers," because an imaginary line drawn
northward through them indicates the Pole Star.

Now it has been found that five of these stars — viz.,
Merak, Phaed, Megrez, Alioth, and Mizar (with its
comrade) — are moving with practically the same speed
in an easterly direction, while the other two, Dubhe
and Benetnasch, are simultaneously moving west-
ward, the motion of Benetnasch being apparently
the more rapid. The consequence of these opposed
motions is, of course, that the figure of the "Dipper"
cannot always have existed and will not continue to
exist. In the accompanying diagrams it has been
thought interesting to show the relative positions of
these seven stars, as seen from the point which the
earth now occupies, both in the past and in the future.
Arrows attached to the stars in the figure representing
the present appearance of the "Dipper" indicate the
directions of the motions and the distances over which
they will carry the stars in a period of about five
hundred centuries. The time, no doubt, seems long,
but remember the vast stretch of ages through which
the earth has passed, and then reflect that no reason
is apparent why our globe should not continue to be
a scene of animation for ten thousand centuries yet
to come. The fact that the little star Alcor placed
so close to Mizar should accompany the latter in its
flight is not surprising, but that two of the principal
stars of the group should be found moving in a direc-
tion exactly opposed to that pursued by the other five
is surprising in the highest degree; and it recalls the

59

CURIOSITIES OF THE SKY

strange theory of a double drift affecting all the stars,
to which attention was called in the preceding chapter.
It would appear that Benetnasch and Dubhe belong

CASSIOPEIA AT PRESENT

CASSIOPEIA IN THE FUTURE

to one "current," and Merak, Phaed, Megrez, Alioth,
and Mizar to the other. As far as is known, the mo-
tions of the seven stars are not shared by the smaller

60

PASSING OF THE CONSTELLATIONS

stars scattered about them, but on the theory of cur-
rents there should be such community of motion,
and further investigation may reveal it.

From the "Great Dipper" we turn to a constella-
tion hardly less conspicuous and situated at an equal
distance from the pole on the other side — Cassiopeia.
This famous star-group commemorating the romantic
Queen of Ethiopia whose vain boasting of her beauty
was punished by the exposure of her daughter
Andromeda to the "Sea Monster," is well marked
by five stars which form an irregular letter "W"
with its open side toward the pole. Three of these
stars are usually ranked as of the second magnitude,
and two of the third; but to ordinary observation
they appear of nearly equal brightness, and present
a very striking picture. They mark out the chair
and a part of the figure of the beautiful queen. Be-
ginning at the right-hand, or western, end of the
"W," their Greek letter designations are: Beta (j3),
Alpha (a), Gamma (y), Delta (S), and Epsilon (e).
Four of them, Beta, Alpha, Delta, and Epsilon are
travelling eastwardly at various speeds, while the fifth,
Gamma, moves in a westerly direction. The motion
of Beta is more rapid than that of any of the others.
It should be said, however, that no little uncertainty
attaches to the estimates of the rate of motion of
stars which are not going very rapidly, and different
observers often vary considerably in their results.

In the beautiful "Northern Crown," one of the
most perfect and charming of all the figures to be
found in the stars, the alternate combining and
scattering effects of the stellar motions are shown by

61

CURIOSITIES OF THE SKY

comparing the appearance which the constellation
must have had five hundred centuries ago with that
which it has at present and that which it will have
in the future. The seven principal stars of the
asterism, forming a surprisingly perfect coronet, have
movements in three directions at right angles to one
another. That in these circumstances they should
ever have arrived at positions giving them so striking
an appearance of definite association is certainly
surprising; from its aspect one would have expected
to find a community of movement governing the
brilliants of the " Crown," but instead of that we find
evidence that they will inevitably drift apart and the
beautiful figure will dissolve.

A similar fate awaits such asterisms as the "North-
ern Cross" in Cygnus; the "Crow" (Corvus), which
stands on the back of the great "Sea Serpent,"
Hydra, and pecks at his scales; "Job's Coffin"
(Delphinus); the "Great Square of Pegasus"; the
"Twins" (Gemini) ; the beautiful "Sickle" in Leo; and
the exquisite group of the Hyades in Taurus. In the
case of the Hyades, two controlling movements are
manifest: one, affecting five of the stars which form
the well-known figure of a letter "V," is directed
northerly; the other, which controls the direction of
two stars, has an easterly trend. The chief star of
the group, Aldebaran, one of the finest of all stars
both for its brilliance and its color, is the most affect-
ed by the easterly motion. In time it will drift en-
tirely out of connection with its present neighbors.
Although the Hyades do not form so compact a group
as the Pleiades in the same constellation, yet their

62

PASSING OF THE CONSTELLATIONS

appearance of relationship is sufficient to awaken a
feeling of surprise over the fact that, as with the stars
of the "Dipper," their association is only temporary or
apparent.

The
Pearl

THE " NORTHERN CROWN " AT
PRESENT

The Pearl

THE "NORTHERN CROWN" IN THE

FUTURE

The Pearl

THE "NORTHERN CROWN" IN THE PAST

The great figure of Orion appears to be more last-
ing, not because its stars are physically connected,
but because of their great distance, which renders

63

CURIOSITIES OF THE SKY

their movements too deliberate to be exactly ascer-
tained. Two of the greatest of its stars, Betelgeusc
and Rigel, possess, as far as has been ascertained,
no perceptible motion across the line of sight, but
there is a little movement perceptible in the "Belt."
At the present time this consists of an almost perfect
straight line, a row of second-magnitude stars about
equally spaced and of the most striking beauty. In
the course of time, however, the two right-hand
stars, Mintaka and Alnilam (how fine are these Arabic
star names!) will approach each other and form a
naked-eye double, but the third, Alnita, will drift
away eastward, so that the "Belt" will no longer
exist.

For one more example, let us go to the southern
hemisphere, whose most celebrated constellation,
the "Southern Cross," has found a place in all modern
literatures, although it has no claim to consideration
on account of association with ancient legends. This
most attractive asterism, which has never ceased to
fascinate the imagination of Christendom since it was
first devoutly described by the early explorers of the
South, is but a passing collocation of brilliant stars.
Yet even in its transfigurations it has been for hun-
dreds of centuries, and will continue to be for hun-
dreds of centuries to come, a most striking object in
the sky. Our figures show its appearance in three
successive phases : first, as it was fifty thousand years
ago (viewed from the earth's present location) ; second,
as it is in our day ; and, third, as it will be an equal time
in the future. The nearness of these bright stars to
one another — the length of the longer beam of the

64

PASSING OF THE CONSTELLATIONS

"Cross" is only six degrees — makes this group very
noticeable, whatever the arrangement of its com-
ponents may be. The largest star, at the base of the
"Cross," is of the first magnitude, two of the others
are of the second magnitude, and the fourth is of
the third. Other stars, not represented in the figures,

THE "SOUTHERN CROSS " THE "SOUTHERN CROSS

AS IT IS AS IT WILL BE

THE " SOUTHERN CROSS " AS IT ONCE WAS

increase the effect of a celestial blazonry, although
they do not help the resemblance to a cross.

But since the motion of the solar system itself will,
in the course of so long a period as fifty thousand
years, produce a great change in the perspective of
the heavens as seen from the earth, by carrying us
nearly nineteen trillion miles from our present place,

65

CURIOSITIES OF THE SKY

why, it may be asked, seek to represent future ap-
pearances of the constellations which we could not
hope to see, even if we could survive so long? The
answer is : Because these things aid the mind to form
a picture of the effects of the mobility of the starry
universe. Only by showing the changes from some
definite point of view can we arrive at a due com-
prehension of them. The constellations are more or
less familiar to everybody, so that impending changes
of their forms must at once strike the eye and the
imagination, and make clearer the significance of the
movements of the stars. If the future history of
mankind is to resemble its past and if our race is
destined to survive yet a million years, then our
remote descendants will see a "new heavens" if not
a "new earth," and will have to invent novel con-
stellations to perpetuate their legends and my-
thologies.

If our knowledge of the relative distances of the
stars were more complete, it would be an interesting
exercise in celestial geometry to project the con-
stellations probably visible to the inhabitants of
worlds revolving around some of the other suns of
space. Our sun is too insignificant for us to think
that he can make a conspicuous appearance among
them, except, perhaps, in a few cases. As seen,
for instance, from the nearest known star, Alpha
Centauri, the sun would appear of the average first
magnitude, and consequently from that standpoint
he might be the gem of some little constellation which
had no Sirius, or Arcturus, or Vega to eclipse him with
its superior splendor. But from the distance of the

66

PASSING OF THE CONSTELLATIONS

vast majority of the stars the sun would probably be
invisible to the naked eye, and as seen from nearer
systems could only rank as a fifth or sixth magnitude
star, unnoticed and unknown except by the star-
charting astronomer.

CONFLAGRATIONS IN THE HEAVENS

SUPPOSE it were possible for the world to take
fire and burn up — as some pessimists think that
it will do when the Divine wrath shall have sufficiently
accumulated against it — nobody out of our own little
corner of space would ever be aware of the catastrophe !
With all their telescopes, the astronomers living in the
golden light of Arcturus or the diamond blaze of
Canopus would be unable to detect the least glimmer
of the conflagration that had destroyed the seat of
Adam and his descendants, just as now they are
totally ignorant of its existence.

But at least fifteen times in the course of recorded
history men looking out from the earth have beheld
in the remote depths of space great outbursts of fiery
light, some of them more splendidly luminous than
anything else in the firmament except the sun! If
they were conflagrations, how many million worlds
like ours were required to feed their blaze ?

It is probable that " temporary" or "new" stars,
as these wonderful apparitions are called, really are
conflagrations; not in the sense of a bonfire or a burn-
ing house or city, but in that of a sudden eruption of
inconceivable heat and light, such as would result

68

CONFLAGRATIONS

from the stripping off the shell of an encrusted sun
or the crashing together of two mighty orbs flying
through space with a hundred times the velocity of
the swiftest cannon-shot.

Temporary stars are the rarest and most erratic
of astronomical phenomena. The earliest records
relating to them are not very clear, and we cannot in
every instance be certain that it was one of these
appearances that the ignorant and superstitious old
chroniclers are trying to describe. The first tem-
porary star that we are absolutely sure of appeared
in 1572, and is known as "Tycho's Star," because the
celebrated Danish astronomer (whose remains, with
his gold-and-silver artificial nose — made necessary
by a duel — still intact, were disinterred and reburied
in 1901) was the first to perceive it in the sky, and the
most assiduous and successful in his studies of it.
As the first fully accredited representative of its class,
this new star made its entry upon the scene with
becoming eclat. It is characteristic of these phenom-
ena that they burst into view with amazing sudden-
ness, and, of course, entirely unexpectedly. Tycho's
star appeared in the constellation Cassiopeia, near
a now well-known and much- watched little star named
Kappa, on the evening of November n, 1572. The
story has often been repeated, but it never loses in-
terest, how Tycho, going home that evening, saw
people in the street pointing and staring at the
sky directly over their heads, and following the direc-
tion of their hands and eyes he was astonished to see,
near the zenith, an unknown star of surpassing brill-
iance. It outshone the planet Jupiter, and was there-

69

CURIOSITIES OF THE SKY

fore far brighter than the first magnitude. There was
not another star in the heavens that could be compared
with it in splendor. Tycho was not in all respects free
from the superstitions of his time — and who is ? — but
he had the true scientific instinct, and immediately he
began to study the stranger, and to record with the
greatest care every change in its aspect. First he de-
termined as well as he could with the imperfect in-
struments of his day, many of which he had himself
invented, the precise location of the phenomenon in
the sky. Then he followed the changes that it under-
went. At first it brightened until its light equalled
or exceeded that of the planet Venus at her bright-
est, a statement which will be appreciated at its full
value by any one who has ever watched Venus when
she plays her dazzling role of "Evening Star," flaring
like an arc light in the sunset sky. It even became
so brilliant as to be visible in full daylight, since, its
position being circumpolar, it never set in the latitude
of Northern Europe. Finally it began to fade, turn-
ing red as it did so, and in March, 1574, it disappeared
from Tycho's searching gaze, and has never been seen
again from that day to this. None of the astronomers
of the time could make anything of it. They had not
yet as many bases of speculation as we possess to-day.
Tycho's star has achieved a romantic reputation by
being fancifully identified with the "Star of Bethle-
hem, " said to have led the wrondering Magi from their
eastern deserts to the cradle-manger of the Savior in
Palestine. Many attempts have been made to
connect this traditional "star" with some known
phenomenon of the heavens, and none seems more

70

\ 5

\ ^ *

v x , *

\ \ •

\ \

\ / >-

\ / «

\ /

\ /

\ Camelopardalis /

•f

I
\ • / ^>^

'iga

/ ' \

\ / x

•

c v ' *

• •

e//a \ t

.---' _ / ** •*

/' • ' "^ *t *r

''

.* i \

Perseus w \

Cepheus

\, • N

x

\

,\ Cassiopeia

CHART SHOWING LOCATION OF TYCHO's STAR, 1572, AND NOVA
PERSEI OF 1901

CONFLAGRATIONS

idle than this. Yet it persistently survives, and no
astronomer is free from eager questions about it ad-
dressed by people whose imagination has been excited
by the legend. It is only necessary to say that the
supposition of a connection between the phenomenon
of the Magi and Tycho's star is without any scien-
tific foundation. It was originally based upon an
unwarranted assumption that the star of Tycho was
a variable of long period, appearing once every three
hundred and fifteen years, or thereabout. If that
were true there would have been an apparition some-
where near the traditional date of the birth of Christ,
a date which is itself uncertain. But even the data
on which the assumption was based are inconsistent
with the theory. Certain monkish records speak of
something wonderful appearing in the sky in the years
1264 and 945, and these were taken to have been
outbursts of Tycho's star. Investigation shows that
the records more probably refer to comets, but even
if the objects seen were temporary stars, their dates
do not suit the hypothesis; from 945 to 1264 there is
a gap of 319 years, and from 1264 to 1572 one of only
308 years; moreover, 337 years have now (1909)
elapsed since Tycho saw the last glimmer of his star.
Upon a variability so irregular and uncertain as that,
even if we felt sure that it existed, no conclusion could
be found concerning an apparition occurring 2000
years ago.

In the year 1600 (the year in which Giordano Bruno

was burned at the stake for teaching that there is

more than one physical world) , a temporary star of the

third magnitude broke out in the constellation Cygnus,

V 73

CURIOSITIES OF THE SKY

and curiously enough, considering the rarity of such
phenomena, only four years later another surprisingly
brilliant one appeared in the constellation Ophiuchus.
This is of ten called " Kepler's Star/' because the great
German astronomer devoted to it the same attention
that Tycho had given to the earlier phenomenon.
It, too, like Tycho's, was at first the brightest object
in the stellar heavens, although it seems never to have
quite equalled its famous predecessor in splendor.
It disappeared after a year, also turning of a red color
as it became more faint. We shall see the significance
of this as we go on. Some of Kepler's contemporaries
suggested that the outburst of this star was due to a
meeting of atoms in space, an idea bearing a striking
resemblance to the modern theory of "astronomical
collisions."

In 1670, 1848, and 1860 temporary stars made their
appearance, but none of them was of great brilliance.
In 1866 one of the second magnitude broke forth in
the "Northern Crown" and awoke much interest,
because by that time the spectroscope had begun
to be employed in studying the composition of the
stars, and Huggins demonstrated that the new star
consisted largely of incandescent hydrogen. But
this star, apparently unlike the others mentioned, was
not absolutely new. Before its outburst it had shone
as a star of the ninth magnitude (entirely invisible,
of course, to the naked eye) , and after about six weeks
it faded to its original condition in which it has
ever since remained. In 1876 a temporary star ap-
peared in the constellation Cygnus, and attained at
one time the brightness of the second magnitude.

74

CONFLAGRATIONS

Its spectrum and its behavior resembled those of its
immediate predecessor. In 1885 astronomers were
surprised to see a sixth-magnitude star glimmering
in the midst of the hazy cloud of the great Andromeda
Nebula. It soon absolutely disappeared. Its spec-
trum was remarkable for being "continuous," like
that of the nebula itself. A continuous spectrum is
supposed to represent a body, or a mass, which is
either solid or liquid, or composed of gas under great
pressure. In January, 1892, a new star was suddenly
seen in the constellation Auriga. It never rose much
above the fourth magnitude, but it showed a peculiar
spectrum containing both bright and dark lines of
hydrogen.

But a bewildering surprise was now in store; the
world was to behold at the opening of the twentieth
century such a celestial spectacle as had not been on
view since the times of Tycho and Kepler. Before
daylight on the morning of February 22, 1901, the
Rev. Doctor Anderson, of Edinburgh, an amateur
astronomer, who had also been the first to see the new
star in Auriga, beheld a strange object in the con-
stellation Perseus not far from the celebrated variable
star Algol. He recognized its character at once, and
immediately telegraphed the news, which awoke the
startled attention of astronomers all over the world.
When first seen the new star was no brighter than
Algol (less than the second magnitude), but within
twenty-four hours it was ablaze, outshining even the
brilliant Capella, and far surpassing the first magni-
tude. At the spot in the sky where it appeared noth-
ing whatever was visible on the night before its com-

75

CURIOSITIES OF THE SKY

ing. This is known with certainty because a photo-
graph had been made of that very region on Feb-
ruary 21, and this photograph showed everything
down to the twelfth magnitude, but not a trace of the
stranger which burst into view between the 2ist and
the 22d like the explosion of a rocket.

Upon one who knew the stars the apparition of this
intruder in a well-known constellation had the effect
of a sudden invasion. The new star was not far west
of the zenith in the early evening, and in that position
showed to the best advantage. To see Capella, the
hitherto unchallenged ruler of that quarter of the
sky, abased by comparison with this stranger of alien
aspect, for there was always an unfamiliar look about
the "nova," was decidedly disconcerting. It seemed
to portend the beginning of a revolution in the heavens.
One could understand what the effect of such an
apparition must have been in the superstitious times
of Tycho. The star of Tycho had burst forth on the
northern border of the Milky Way; this one was on
its southern border, some forty-five degrees farther
east.

Astronomers were well prepared this time for the
scientific study of the new star, both astronomical
photography and spectroscopy having been perfected,
and the results of their investigations were calculated
to increase the wonder with which the phenomenon
was regarded. The star remained at its brightest
only a few days • then, like a veritable conflagration, it
began to languish • and, like the reflection of a dying
fire, as it sank it began to glow with the red color of
embers. But its changes were spasmodic ; once about

76

CONFLAGRATIONS

every three days it flared up only to die away again.
During these fluctuations its light varied alternately
in the ratio of one to six. Finally it took a permanent
downward course, and after a few months the naked
eye could no longer perceive it; but it remained
visible with telescopes, gradually fading until it had
sunk to the ninth magnitude. Then another as-
tonishing change happened: in August photographs
taken at the Yerkes Observatory and at Heidelberg
showed that the "nova" was surrounded by a spiral
nebula! The nebula had not been there before,
and no one could doubt that it represented a phase
of the same catastrophe that had produced the out-
burst of the new star. At one time the star seemed
virtually to have disappeared, as if all its substance
had been expanded into the nebulous cloud, but
always there remained a stellar nucleus about which
the misty spiral spread wider and ever wider, like a
wave expanding around a centre of disturbance. The
nebula too showed a variability of brightness, and four
condensations which formed in it seemed to have a
motion of revolution about the star. As time went
on the nebula continued to expand at a rate which
was computed to be not less than twenty thousand
miles per second! And now the star itself, showing
indications of having turned into a nebula, behaved
in av most erratic manner, giving rise to the suspicion
that it was about to burst out again. But this did
not occur, and at length it sunk into a state of lethargy
from which it has to the present time not recovered.
But the nebulous spiral has disappeared, and the
entire phenomenon as it now (1909) exists consists

77

CURIOSITIES OF THE SKY

of a faint nebulous star of less than the ninth magni-
tude.

The wonderful transformations just described had
been forecast in advance of the discovery of the
nebulous spiral encircling the star by the spectro-
scopic study of the latter. At first there was no sug-
gestion of a nebular constitution, but within a month
or two characteristic nebular lines began to appear,
and in less than six months the whole spectrum had
been transformed to the nebular type. In the mean
time the shifting of the spectral lines indicated a com-
plication of rapid motions in several directions simul-
taneously. These motions were estimated to amount
to from one hundred to five hundred miles per second.

The human mind is so constituted that it feels
forced to seek an explanation of so marvellous a
phenomenon as this, even in the absence of the data
needed for a sound conclusion. The most natural
hypothesis, perhaps, is that of a collision. Such a
catastrophe could certainly happen. It has been
shown, for instance, that in infinity of time the earth
is sure to be hit by a comet ; in the same way it may
be asserted that, if no time limit is fixed, the sun is
certain to run against some obstacle in space, either
another star, or a dense meteor swarm, or one of the
dark bodies which there is every reason to believe
abound around us. The consequences of such a
collision are easy to foretell, provided that we know
the masses and the velocities of the colliding bodies.
In a preceding chapter we have discussed the motions
of the sun and stars, and have seen that they are so
swift that an encounter between any two of them

CONFLAGRATIONS

could not but be disastrous. But this is not all;
for as soon as two stars approached within a few
million miles their speed would be enormously in-
creased by their reciprocal attractions and, if their
motion was directed radially with respect to their
centres, they would come together with a crash that
would reduce them both to nebulous clouds. It is
true that the chances of such a "head-on*' collision
are relatively very small; two stars approaching each
other would most probably fall into closed orbits
around their common centre of gravity. If there
were a collision it would most likely be a grazing one
instead of a direct front-to-front encounter. But
even a close approach, without any actual collision,
would probably prove disastrous, owing to the tidal
influence of each of the bodies upon the other. Suns,
in consequence of their enormous masses and di-
mensions and the peculiarities of their constitution,
are exceedingly dangerous to one another at close
quarters. Propinquity awakes in them a mutually
destructive tendency. Consisting of matter in the
gaseous, or perhaps, in some cases, liquid, state, their
tidal pull upon each other if brought close together
might burst them asunder, and the photospheric
envelope being destroyed the internal incandescent
mass would gush out, bringing fiery death to any
planets that were revolving near. Without regard
to the resulting disturbance of the earth's orbit, the
close approach of a great star to the sun would be in
the highest degree perilous to us. But this is a danger
which may properly be regarded as indefinitely re-
mote, since, at our present location in space, we are

79

CURIOSITIES OF THE SKY

certainly far from every star except the sun, and we
may feel confident that no great invisible body is
near, for if there were one we should be aware of its
presence from the effects of its attraction. As to
dark nebulae which may possibly lie in the track that
the solar system is pursuing at the rate of 375,000,000
miles per year, that is another question — and they, too,
could be dangerous!

This brings us directly back to "Nova Persi," for
among the many suggestions offered to explain its
outburst, as well as those of other temporary stars,
one of the most fruitful is that of a collision between
a star and a vast invisible nebula. Professor Seeliger,
of Munich, first proposed this theory, but it afterward
underwent some modifications from others. Stated
in a general form, the idea is that a huge dark body,
perhaps an extinguished sun, encountered in its
progress through space a widespread flock of small
meteors forming a dark nebula. As it plunged into
the swarm the friction of the innumerable collisions
with the meteors heated its surface to incandescence,
and being of vast size it then became visible to us as a
new star. Meanwhile the motion of the body through
the nebula, and its rotation upon itself, set up a
gyration in the blazing atmosphere formed around it
by the vaporized meteors; and as this atmosphere
spread wider, under the laws of gyratory motion a
rotation in the opposite direction began in the in-
flamed meteoric cloud outside the central part of the
vortex. Thus the spectral lines were caused to show
motion in opposite directions, a part of the incan-
descent mass approaching the earth simultaneously

Bo

CONFLAGRATIONS

with the retreat of another part. So the curious
spectroscopic observations before mentioned were ex-
plained. This theory might also account for the
appearance of the nebulous spiral first seen some six
months after the original outburst. The sequent
changes in the spectrum of the "nova" are accounted
for by this theory on the assumption, reasonable
enough in itself, that at first the invading body would
be enveloped in a vaporized atmosphere of relatively
slight depth, producing by its absorption the fine
dark lines first observed* but that as time went on
and the incessant collisions continued, the blazing
atmosphere would become very deep and extensive,
whereupon the appearance of the spectral lines would
change, and bright lines due to the light of the in-
candescent meteors surrounding the nucleus at a
great distance would take the place of the original
dark ones. The vortex of meteors once formed
would protect the flying body within from further
immediate collisions, the latter now occurring mainly
among the meteors themselves, and then the central
blaze would die down, and the original splendor of the
phenomenon would fade.

But the theories about Nova Persei have been
almost as numerous as the astronomers who have
speculated about it. One of the most startling of
them assumed that the outburst was caused by the
running amuck of a dark star which had encountered
another star surrounded with planets, the renewed
outbreaks of light after the principal one had faded
being due to the successive running down of the un-
fortunate planets! Yet another hypothesis is based

83

CURIOSITIES OF THE SKY

on what we have already said of the tidal influence
that two close approaching suns would have upon
each other. Supposing two such bodies which had
become encrusted, but remained incandescent and
fluid within, to approach within almost striking dis-
tance; they would whirl each other about their com-
mon centre of gravity, and at the same time their
shells would burst under the tidal strain, and their
glowing nuclei being disclosed would produce a great
outburst of light. Applying this theory to a "nova/*
like that of 1866 in the "Northern Crown," which
had been visible as a small star before the outbreak,
and which afterward resumed its former aspect, we
should have to assume that a yet shining sun had
been approached by a dark body whose attraction
temporarily burst open its photosphere. It might
be supposed that in this case the dark body was too
far advanced in cooling to suffer the same fate from
the tidal pull of its victim. But a close approach of
that kind would be expected to result in the forma-
tion of a binary system, with orbits of great eccentri-
city, perhaps, and after the lapse of a certain time the
outburst should be renewed by another approxima-
tion of the two bodies. A temporary star of that
kind would rather be ranked as a variable.

The celebrated French astronomer, Janssen, had a
different theory of Nova Persei, and of temporary
stars in general. According to his idea, such phe-
nomena might be the result of chemical changes
taking place in a sun without interference by, or
collision with, another body. Janssen was engaged
for many years in trying to discover evidence of the

84

CONFLAGRATIONS

existence of oxygen in the sun, and he constructed his
observatory on the summit of Mont Blanc specially
to pursue that research. He believed that oxygen
must surely exist in the sun since we find so many other
familiar elements included in the constitution of the
solar globe, and as he was unable to discover satis-
factory evidence of its presence he assumed that it
existed there in a form unknown on the earth. If
it were normally in the sun's chromosphere, or
coronal atmosphere, he said, it would combine with
the hydrogen which we know is there and form an
obscuring envelope of water vapor. It exists, then,
in a special state, uncombined with hydrogen; but
let the temperature of the sun sink to a critical point
and the oxygen will assume its normal properties and
combine with the hydrogen, producing a mighty out-
burst of light and heat. This, Janssen thought,
might explain the phenomena of the temporary stars.
It would also, he suggested, account for their brief
career, because the combination of the elements would
be quickly accomplished, and then the resulting water
vapor would form an atmosphere cutting off the
radiation from the star within.

This theory may be said to have a livelier human
interest than some of the others, since, according to it,
the sun may carry in its very constitution a menace
to mankind; one does not like to think of it being sud-
denly transformed into a gigantic laboratory for the
explosive combination of oxygen and hydrogen!
But while Janssen' s theory might do for some tem-
porary stars, it is inadequate to explain all the
phenomena of Nova Persei, and particularly the

85

CURIOSITIES OF THE SKY

appearance of the great spiral nebula that seemed to
exhale from the heart of the star. Upon the whole,
the theory of an encounter between a star and a dark
nebula seems best to fit the observations. By that
hypothesis the expanding billow of light surrounding
the core of the conflagration is very well accounted
for, and the spectroscopic peculiarities are also ex-
plained.

Dr. Gustav Le Bon offers a yet more alarming
theory, suggesting that temporary stars are the
result of atomic explosion; but we shall touch upon
this more fully in Chapter XIV.

Twice in the course of this discussion we have
called attention to the change of color invariably
undergone by temporary stars in the later stages of
their career. This was conspicuous with Nova
Persei which glowed more and more redly as it faded,
until the nebulous light began to overpower that of
the stellar nucleus. Nothing could be more sugges-
tive of the dying out of a great fire. Moreover,
change of color from white to red is characteristic of
all variable stars of long period, such as "Mira" in
Cetus. It is also characteristic of stars believed to
be in the later stages of evolution, and consequently
approaching extinction, like Antares and Betelgeuse,
and still more notably certain small stars which
"gleam like rubies in the field of the telescope."
These last appear to be suns in the closing period of
existence as self-luminous bodies. Between the white
stars, such as Sirius and Rigel, and the red stars, such
as Aldebaran and Alpha Herculis, there is a pro-
gressive series of colors from golden yellow through

86

CONFLAGRATIONS

orange to deep red. The change is believed to be due
to the increase of absorbing vapors in the stellar
atmosphere as the body cools down. In the case of
ordinary stars these changes no doubt occupy many
millions of years, which represent the average dura-
tion of solar life; but the temporary stars run through
similar changes in a few months: they resemble
ephemeral insects — born in the morning and doomed
to perish with the going down of the sun.

VI

EXPLOSIVE AND WHIRLING NEBULA

ONE of the most surprising triumphs of celestial
photography was Professor Keeler's discovery,
in 1899, that the great majority of the nebulae have a
distinctly spiral form. This form, previously known
in Lord Rosse's great " Whirlpool Nebula," had been
supposed to be exceptional; now the photographs,
far excelling telescopic views in the revelation of
nebular forms, showed the spiral to be the typical
shape. Indeed, it is a question whether all nebulae are
not to some extent spiral. The extreme importance
of this discovery is shown in the effect that it has had
upon hitherto prevailing views of solar and planetary
evolution. For more than three-quarters of a century
Laplace's celebrated hypothesis of the manner of
origin of the solar system from a rotating and con-
tracting nebula surrounding the sun had guided
speculation on that subject, and had been tentatively
extended to cover the evolution of systems in general.
The apparent forms of some of the nebulas which the
telescope had revealed were regarded, and by some
are still regarded, as giving visual evidence in favor
of this theory. There is a "ring nebula" in Lyra
with a central star, and a "planetary nebula" in

88

LORD ROSSE S NEBULA

WHIRLING NEBULA

Gemini bearing no little resemblance to the planet
Saturn with its rings, both of which appear to be
practical realizations of Laplace's idea, and the
elliptical rings surrounding the central condensation
of the Andromeda Nebula may be cited for the same
kind of proof.

But since Keeler's discovery there has been a de-
cided turning of speculation another way. The form
of the spiral nebulae seems to be entirely inconsistent
with the theory of an originally globular or disk-
shaped nebula condensing around a sun and throw-
ing or leaving off rings, to be subsequently shaped
into planets. Some astronomers, indeed, now reject
Laplace's hypothesis in toto, preferring to think that
even our solar system originated from a spiral nebula.
Since the spiral type prevails among the existing
nebulas, we must make any mechanical theory of the
development of stars and planetary systems from
them accord with the requirements which that form
imposes. A glance at the extraordinary variations
upon the spiral which Professor Keeler's photographs
reveal is sufficient to convince one of the difficulty
of the task of basing a general theory upon them. In
truth, it is much easier to criticize Laplace's hypothesis
than to invent a satisfactory substitute for it. If the
spiral nebulae seem to oppose it there are other nebulae
which appear to support it, and it may be that no one
fixed theory can account for all the forms of stellar
evolution in the universe. Our particular planetary
system may have originated very much as the great
French mathematician supposed, while others have
undergone, or are now undergoing, a different process

91

CURIOSITIES OF THE SKY

of development. There is always a too strong
tendency to regard an important new discovery and
the theories and speculations based upon it as revolu-
tionizing knowledge, and displacing or overthrowing
everything that went before. Upon the plea that
''Laplace only made a guess" more recent guesses
have been driven to extremes and treated by in-
judicious exponents as "the solid facts at last."

Before considering more recent theories than La-
place's, let us see what the nature of the photographic
revelations is. The vast celestial maelstrom dis-
covered by Lord Rosse in the "Hunting Dogs" may
be taken as the leading type of the spiral nebulas,
although there are less conspicuous objects of the kind
which, perhaps, better illustrate some of their pe-
culiarities. Lord Rosse's nebula appears far more
wonderful in the photographs than in his drawings
made with the aid of his giant reflecting telescope at
Parsonstown, for the photographic plate records
details that no telescope is capable of showing.
Suppose we look at the photograph of this object as
any person of common sense would look at any great
and strange natural phenomenon. What is the first
thing that strikes the mind? It is certainly the ap-
pearance of violent whirling motion. One would say
that the whole glowing mass had been spun about with
tremendous velocity, or that it had been set rotating
so rapidly that it had become the victim of "centrif-
ugal force," one huge fragment having broken loose
and started to gyrate off into space. Closer inspec-
tion shows that in addition to the principal focus
there are various smaller condensations scattered

92

WONDERFUL SPIRAL IN TRIANGULUM

WHIRLING NEBULA

through the mass. These are conspicuous in the
spirals. Some of them are stellar points, and but for
the significance of their location we might suppose
them to be stars which happen to lie in line between
us and the nebula. But when we observe how many
of them follow most faithfully the curves of the
spirals we cannot but conclude that they form an
essential part of the phenomenon; it is not possible
to believe that their presence in such situations is
merely fortuitous. One of the outer spirals has at
least a dozen of these star-like points strung upon it;
some of them sharp, small, and distinct, others more
blurred and nebulous, suggesting different stages of
condensation. Even the part which seems to have
been flung loose from the main mass has, in addition
to its central condensation, at least one stellar point
gleaming in the half-vanished spire attached to
it. Some of the more distant stars scattered around
the "whirlpool" look as if they too had been shot out
of the mighty vortex, afterward condensing into un-
mistakable solar bodies. There are at least two
curved rows of minute stars a little beyond the
periphery of the luminous whorl which clearly follow
lines concentric with those of the nebulous spirals.
Such facts are simply dumfounding for any one who
will bestow sufficient thought upon them, for these
are suns, though they may be small ones ; and what a
birth is that for a sun!

Look now again at the glowing spirals. We ob-
serve that hardly have they left the central mass be-
fore they begin to coagulate. In some places they
have a "ropy" aspect; or they are like peascods filled
6 95

CURIOSITIES OF THE SKY

with growing seeds, which eventually will become
stars. The great focus itself shows a similar tendency,
especially around its circumference. The sense that
it imparts of a tremendous shattering force at w^ork
is overwhelming. There is probably more matter in
that whirling and bursting nebula than would suffice
to make a hundred solar systems! It must be con-
fessed at once that there is no confirmation of the
Laplacean hypothesis here; but what hypothesis will
fit the facts ? There is one which it has been claimed
does so, but we shall come to that later. In the
meanwhile, as a preparation, fix in the memory the
appearance of that second spiral mass spinning be-
side its master which seems to have spurned it
away.

For a second example of the spiral nebulas look at
the one in the constellation Triangulum. Go d, haw
hath the imagination of puny man failed to comprehend
Thee! Here is creation through destruction with a
vengeance! The spiral form of the nebula is un-
mistakable, but it is half obliterated amid the turmoil
of flying masses hurled away on all sides with tornadic
fury. The focus itself is splitting asunder under the
intolerable strain, and in a little while, as time is
reckoned in the Cosmos, it will be gyrating into stars.
And then look at the cyclonic rain of already finished
stars whirling round the outskirts of the storm.
Observe how scores of them are yet involved in the
fading streams of the nebulous spirals; see how they
have been thrown into vast loops and curves, of a
beauty that half redeems the terror of the spectacle
enclosed within their lines — like iridescent cirri hover-

96

SPIRAL IN URSA MAJOR

WHIRLING NEBULA

ing about the edges of a hurricane. And so again
are suns born!

Let us turn to the exquisite spiral in Ursa Major;
how different its aspect from that of the other! One
would say that if the terrific coil in Triangulum has
all but destroyed itself in its fury, this one on the con-
trary has just begun its self-demolition. As one
gazes one seems to see in tt the smooth, swift, accelerat-
ing motion that precedes catastrophe. The central
part is still intact, dense, and uniform in texture.
How graceful are the spirals that smoothly rise from
its oval rim and, gemmed with little stars, wind off
into the darkness until they have become as delicate
as threads of gossamer! But at bottom the story told
here is the same — creation by gyration!

Compare with the above the curious mass in Cetus.
Here the plane of the whirling nebula nearly coincides
with our line of sight and we see the object at a low
angle. It is far advanced and torn to shreds, and if
we could look at it perpendicularly to its plane it is .
evident that it would closely resemble the spectacle
in Triangulum.

Then take the famous Andromeda Nebula (see
Frontispiece), which is so vast that notwithstanding ;
its immense distance even the naked eye perceives it j
as an enigmatical wisp in the sky. Its image on the j
sensitive plate is the masterpiece of astronomical pho j
tography; for wild, incomprehensible beauty there is j
nothing that can be compared with it. Here, if any- I
where, we look upon the spectacle of creation in one of
its earliest stages. The Andromeda Nebula is appar-
ently less advanced toward transformation into stellar

99

CURIOSITIES OF THE SKY

bodies than is that in Triangulum. The immense
crowd of stars sprinkled over it and its neighborhood
seem in the main to lie this side of the nebula, and con-
sequently to have no connection with it. But incip-
ient stars (in some places clusters of them) are seen
in the nebulous rings, while one or two huge masses
seem to give promise of transformation into stellar
bodies of unusual magnitude. I say "rings" because
although the loops encompassing the Andromeda Neb-
ebula have been called spirals by those who wish ut-
terly to demolish Laplace's hypothesis, yet they are not
manifestly such, as can be seen on comparing them
with the undoubted spirals of the Lord Rosse Nebula.
They look quite as much like circles or ellipses seen at
an angle of, say, fifteen or twenty degrees to their
plane. If they are truly elliptical they accord fairly
well with Laplace's idea, except that the scale of
magnitude is stupendous, and if the Andromeda
Nebula is to become a solar system it will surpass ours
in grandeur beyond all possibility of comparison.

There is one circumstance connected with the spiral
nebulae, and conspicuous in the Andromeda Nebula
on account of its brightness, which makes the ques-
tion of their origin still more puzzling ; they all show
continuous spectra, which, as we have before remarked,
indicate that the mass from which the light comes is
either solid or liquid, or a gas under heavy pressure.
Thus nebulae fall into two classes: the "white"
nebulae, giving a continuous spectrum; and the
"green" nebulas whose spectra are distinctly gaseous.
The Andromeda Nebula is the great representative
of the former class and the Orion Nebula of the latter.

100

NEBULA IN CETUS

WHIRLING NEBULAE

The spectrum of the Andromeda Nebula has been
interpreted to mean that it consists not of luminous
gas, but of a flock of stars so distant that they are
separately indistinguishable even with powerful tele-
scopes, just as the component stars of the Milky Way
are indistinguishable with the naked eye; and upon
this has been based the suggestion that what we see
in Andromeda is an outer universe whose stars form
a series of elliptical garlands surrounding a central
mass of amazing richness. But this idea is unac-
ceptable if for no other reason than that, as just said,
all the spiral nebulas possess the same kind of spec-
trum, and probably no one would be disposed to re-
gard them all as outer universes. As we shall see later,
the peculiarity of the spectra of the spiral nebulas is
appealed to in support of a modern substitute for
Laplace's hypothesis.

Finally, without having by any means exhausted
the variety exhibited by the spiral nebulae, let us
turn to the great representative of the other species,
the Ori^2_J^ebula. In some ways this is even more
marvellous thaiTthe others. The early drawings with
the telescope failed to convey an adequate con-
ception either of its sublimity or of its complication
of structure. It exists in a nebulous region of space,
since photographs show that nearly the whole con-
stellation is interwoven with faintly luminous coils.
To behold the entry of the great nebula into the field
even of a small telescope is a startling experience which
never loses its novelty. As shown by the photo-
graphs, it is an inscrutable chaos of perfectly amazing
extent, where spiral bands, radiating streaks, dense

103

CURIOSITIES OF THE SKY

masses, and dark yawning gaps are strangely inter-
mingled without apparent order. In one place four
conspicuous little stars, better seen with a telescope
than in the photograph on account of the blurring
produced by over-exposure, are suggestively situated
in the midst of a dark opening, and no observer has
ever felt any doubt that these stars have been formed
from the substance of the surrounding nebula. There
are many other stars scattered over its expanse which
manifestly owe their origin to the same source. But
compare the general appearance of this nebula with
the others that we have studied, and remark the dif-
ference. If the unmistakably spiral nebulae resemble
bursting fly-wheels or grindstones from whose perim-
eters torrents of sparks are flying, the Orion Nebula
rather recalls the aspect of a cloud of smoke and
fragments produced by the explosion of a shell. This
idea is enforced by the look of the outer portion far-
thest from the bright half of the nebula, where sharply
edged clouds with dark spaces behind seem to be
billowing away as if driven by a wind blowing from
the centre.

Next let us consider what scientific speculation has
done in the effort to explain these mysteries. La-
place's hypothesis can certainly find no standing
ground either in the Orion Nebula or in those of a
spiral configuration, whatever may be its situation
with respect to the grand Nebula of Andromeda, or
the "ring'* and "planetary" nebulas. Some other
hypothesis more consonant with the appearances
must be found. Among the many that have been
proposed the most elaborate is the " PlanetesimaJ

104

THE ORION NEBULA

WHIRLING NEBULAE

Hypothesis" of Professors Chamberlin and Moulton.
It is to be remarked that it applies to the spiral
nebulae distinctively, and not to an apparently chaotic
mass of gas like the vast luminous cloud in Orion.
The gist of the theory is that these curious objects
are probably the result of close approaches to each
other of two independent suns, reminding us of what
was said on this subject when we were dealing with
temporary stars. Of the previous history of these
appulsing suns the theory gives us no account ; they are
simply supposed to arrive within what may be called
an effective tide-producing distance, and then the
drama begins. Some of the probable consequences
of such an approach have been noticed in Chapter V;
let us now consider them a little more in detail.

Tides always go in couples ; if there is a tide on one
side of a globe there will be a corresponding tide on*
the other side. The cause is to be found in the law
that the force of gravitation varies inversely as the
square of the distance; the attraction on the nearest
surface of a body exercised by another body -is
greater than on its centre, and greater yet than on its
opposite surface. If two great globes attract each
other, each tends to draw the other out into an
ellipsoidal figure; they must be more rigid than steel
to resist this — and even then they cannot altogether
resist. If they are liquid or gaseous they will yield
readily to the force of distortion, the amount of which
will depend upon their distance apart, for the nearer
they are the greater becomes the tidal strain. If
they are encrusted without and liquid or gaseous in
the interior, the internal mass will strive to assume

107

CURIOSITIES OF THE SKY

the figure demanded by the tidal force, and will, if it
can, burst the restraining envelope. Now this is
virtually the predicament of the body we call a sun
when in the immediate presence of another body of
similarly great mass. Such a body is presumably
gaseous throughout, the component gases being held
in a state of rigidity by the compression produced by
the tremendous gravitational force of their own
aggregate mass. At the surface such a body is en-
veloped in a shell of relatively cool matter. Now
suppose a great attracting body, such as another sun,
to approach near enough for the difference in its
attraction on the two opposite sides of the body
and on its centre to become very great; the conse-
quence will be a tidal deformation of the whole body,
and it will lengthen out along the line of the gravita-
tional pull and draw in at the sides, and if its shell
offers considerable resistance, but not enough to
exercise a complete restraint, it will be violently burst
apart, or blown to atoms, and the internal mass will
leap out on the two opposite sides in great fiery
spouts. In the case of a sun further advanced in
cooling than ours the interior might be composed of
molten matter while the exterior crust had become
rigid like the shell of an egg; then the force of the
"tidal explosion" produced by the appulse of another
sun would be more violent in consequence of the
greater resistance overcome. Such, then, is the
mechanism of the first phase in the history of a spiral
nebula according to the Planetesimal Hypothesis.
Two suns, perhaps extinguished ones, have drawn near
together, and an explosive outburst has occurred in

108

WHIRLING NEBULA

one or both. The second phase calls for a more agile
exercise of the imagination.

To simplify the case, let us suppose that only one
of the tugging suns is seriously affected by the strain.
Its vast wings produced by the outburst are twisted
into spirals by their rotation and the contending
attractions exercised upon them, as the two suns, like
battleships in desperate conflict, curve round each
other, concentrating their destructive energies. Then
immense quantities of debris are scattered about in
which eddies are created, and finally, as the sun that
caused the damage goes on its way, leaving its victim
to repair its injuries as it may, the dispersed matter
cools, condenses, and turns into streams of solid
particles circling in elliptical paths about their parent
sun. These particles, or fragments, are the "plane-
tesimals" of the theory. In consequence of the in-
evitable intersection of the orbits of the planetesimals,
nodes are formed where the flying particles meet, and
at these nodes large masses are gradually accumulated.
The larger the mass the greater its attraction, and at
last the nodal points become the nuclei of great
aggregations from which planets are shaped.

This, in very brief form, is the Planetesimal Hypoth-
esis which we are asked to substitute for that based
on Laplace's suggestion as an explanation of the mode
of origin of the solar system; and the phenomena of
the spiral nebulae are appealed to as offering evident
support to the new hypothesis. We are reminded
that they are elliptical in outline, which accords with
the hypothesis; that their spectra are not gaseous,
which shows that they may be composed of soli4

109

CURIOSITIES OF THE SKY

particles like the plahetesimals ; and that their central
masses present an oval form, which is what would
result from the tidal effects, as just described. We
also remember that some of them, like the Lord Rosse
and the Andromeda nebulae, are visually double, and
in these cases we might suppose that the two masses
represent the tide-burst suns that ventured into too
close proximity. It may be added that the authors
of the theory do not insist upon the appulse of two
suns as the only way in which the planetesimals may
have originated, but it is the only supposition that
has been worked out.

But serious questions remain. It needs, for instance,
but a glance at the Triangulum monster to convince
the observer that it cannot be a solar system which
is being evolved there, but rather a swarm of stars.
Many of the detached masses are too vast to admit
of the supposition that they are to be transformed
into planets, in our sense of planets, and the distances
of the stars which appear to have been originally
ejected from the focal masses are too great to allow
us to liken the assemblage that they form to a solar
system. Then, too, no nodes such as the hypothesis
calls for are visible. Moreover, in most of the spiral
nebulas the appearances favor the view that the
supposititious encountering suns have not separated
and gone each rejoicing on its way, after having in-
flicted the maximum possible damage on its opponent,
but that, on the contrary, they remain in close associa-
tion like two wrestlers who cannot escape from each
other's grasp. And this is exactly what the law of
gravitation demands; stars cannot approach one

IIP

WHIRLING NEBULAE

another with impunity, with regard either to their
physical make-up or their future independence of
movement. The theory undertakes to avoid this
difficulty by assuming that in the case of our system
the approach of the foreign body to the sun was not a
close one — just close enough to produce the tidal ex-
trusion of the relatively insignificant quantity of
matter needed to form the planets. But even then
the effect of the appulse would be to change the
direction of flight, both of the sun and of its visitor,
and there is no known star in the sky which can be
selected as the sun's probable partner in their ancient
pas deux. That there are unconquered difficulties
in Laplace's hypothesis no one would deny, but in
simplicity of conception it is incomparably more
satisfactory, and with proper modifications could
probably be made more consonant with existing facts
in our solar system than that which is offered to re-
place it. Even as an explanation of the spiral nebulae,
not as solar systems in process of formation, but as the
birthplaces of stellar clusters, the Planetesimal
Hypothesis would be open to many objections. Grant-
ing its assumptions, it has undoubtedly a strong math-
ematical framework, but the trouble is not with the
mathematics but with the assumptions. Laplace
was one of the ablest mathematicians that ever
lived, but he had never seen a spiral nebula; if he
had, he might have invented a hypothesis to suit its
phenomena. His actual hypothesis was intended
only for our solar system, and he left it in the form of
a "note" for the consideration of his successors, with
the hope that they might be able to discover the full

in

CURIOSITIES OF THE SKY

truth, which he confessed was hidden from him. It
cannot be said that that truth has yet been found,
and when it is found the chances are that intuition
and not logic will have led to it.

The spiral nebulae, then, remain among the greatest
riddles of the universe, while the gaseous nebulas,
like that of Orion, are no less mysterious, although it
seems impossible to doubt that both forms give birth
to stars. It is but natural to look to them for light
on the question of the origin of our planetary system ;
but we should not forget that the scale of the phe-
nomena in the two cases is vastly different, and the
forces in operation may be equally different. A hill
may have been built up by a glacier, while a mountain
may be the product of volcanic forces or of the up-
heaval of the strata of the planet.

VII

THE BANNERS OF THE SUN

A 5 all the world knows the sun, it is a blinding
globe, pouring forth an inconceivable quantity
of light and heat, whose daily passage through the
sky, caused by the earth's rotation on its axis, con-
stitutes the most important phenomenon of terrestrial
existence. Viewed with a dark glass to take off the
glare, or with a telescope, its rim is seen to be a sharp
and smooth circle, and nothing but dark sky is visible
around it. Except for the interference of the moon,
we should probably never have known that there is
any more of the sun than our eyes ordinarily see.

But when an eclipse of the sun occurs, caused by
the interposition of the opaque globe of the moon,
we see its immediate surroundings, which in some
respects are more wonderful than the glowing central
orb. These surroundings, although not in the sense
in which we apply the term to the gaseous envelope
of the earth, may be called the sun's atmosphere.
They consist of two very different parts — first, the
red "prominences," which resemble tongues of flame
ascending thousands of miles above the sun's surface ;
and, second, the "corona," which extends to distances
of millions of miles from the sun, and shines with a

CURIOSITIES OF THE SKY

soft, glowing light. The two combined, when well seen,
make a spectacle without parallel among the marvels
of the sky. Although many attempts have been made
to render the corona visible when there is no eclipse,
all have failed, and it is to the moon alone that we owe
its revelation. To cover the sun's disk with a cir-
cular screen will not answer the purpose because of
the illumination of the air all about the observer.
When the moon hides the sun, on the other hand,
the sunlight is withdrawn from a great cylinder of air
extending to the top of the atmosphere and spreading
many miles around the observer. There is then no
glare to interfere with the spectacle, and the corona
appears in all its surprising beauty. The prominences,
however, although they were discovered during an
eclipse, can now, with the aid of the spectroscope, be
seen f< t any time. But the prominences are rarely
large enough to be noticed by the naked eye, while
the streamers of the corona, stretching far away in
space, like ghostly banners blown out from the black
circle of the obscuring moon, attract every eye, and
to this weird apparition much of the fear inspired
by eclipses has been due. But if the corona has been
a cause of terror in the past it has become a source of
growing knowledge in our time.

The story of the first scientific observation of the
corona and the prominences is thrillingly interesting,
and in fact dramatic. The observation was made
during the eclipse of 1842, which fortunately was
visible all over Central and Southern Europe so that
scores of astronomers saw it. The interest centres
in what happened at Pavia in Northern Italy, where

114

THE CORONA

THE BANNERS OF THE SUN

the English astronomer Francis Baily had set up his
telescope. The eclipse had begun and Baily was busy
at his telescope when, to quote his own words in the
account which he wrote for the Memoirs of the Royal
Astronomical Society: "I was astounded by a tre-
mendous burst of applause from the streets below,
and at the same moment was electrified by the sight
of one of the most brilliant and splendid phenomena
that can well be imagined; for at that instant the
dark body of the moon was suddenly surrounded with
a corona, or kind of bright glory, similar in shape and
magnitude to that which painters draw round the
heads of saints. . . . Pa via contains many thousand
inhabitants, the major part of whom were at this
early hour walking about the streets and squares or
looking out of windows in order to witness this long-
talked-of phenomenon; and when the total obscura-
tion took place, which was instantaneous, there was a
universal shout from every observer which 'made
the welkin ring,' and for the moment withdrew my
attention from the object with which I was imme-
diately occupied. I had, indeed, expected the ap-
pearance of a luminous circle round the moon during
the time of total obscurity; but I did not expect,
from any of the accounts of preceding eclipses that I
had read, to witness so magnificent an exhibition as
that which took place. . . . Splendid and astonishing,
however, as this remarkable phenomenon really was,
and although it could not fail to call forth the admira-
tion and applause of every beholder, yet I must con-
fess that there was at the same time something in its
singular and wonderful appearance that was appalling.

117

CURIOSITIES OF THE SKY

. . . But the most remarkable circumstance attending
the phenomenon was the appearance of three large
protuberances apparently emanating from the circum-
ference of the moon, but evidently forming a portion
of the corona. They had the appearance of moun-
tains of a prodigious elevation; their color was red
tinged with lilac or purple ; perhaps the color of the
peach-blossom would more nearly represent it. They
somewhat resembled the tops of the snowy Alpine
mountains when colored by the rising or the setting
sun. They resembled the Alpine mountains also in
another respect, inasmuch as their light was perfectly
steady, and had none of that flickering or sparkling
motion so visible in other parts of the corona. . . .
The whole of these protuberances were visible even
to the last moment of total obscuration, and when
the first ray of light was admitted from the sun they
vanished, with the corona, altogether, and daylight
was instantly restored."

I have quoted nearly all of this remarkable descrip-
tion not alone for its intrinsic interest, but because
it is the best depiction that can be found of the general
phenomena of a total solar eclipse. Still, not every
such eclipse offers an equally magnificent spectacle.
The eclipses of 1900 and 1905, for instance, which
were seen by the writer, the first in South Carolina and
the second in Spain, fell far short of that described
by Baily in splendor and impressiveness. Of course,
something must be allowed for the effect of surprise;
Baily had not expected to see what was so suddenly
disclosed to him. But both in 1900 and 1905 the
amount of scattered light in the sky was sufficient in

118

THE BANNERS OF THE SUN

itself to make the corona appear faint, and there were
no very conspicuous prominences visible. Yet on
both occasions there was manifest among the specta-
tors that mingling of admiration and awe of which
Baily speaks. The South Carolinians gave a cheer
and the ladies waved their handkerchiefs when the
corona, ineffably delicate of form and texture, melted
into sight and then in two minutes melted away
again. The Spaniards, crowded on the citadel hill
of Burgos, with their king and his royal retinue in
their midst, broke out with a great clapping of hands
as the awaited spectacle unfolded itself in the sky;
and on both occasions, before the applause began,
after an awed silence a low murmur ran through the
crowds. At Burgos it is said many made the sign of
the cross.

It was not long before Baily's idea that the promi-
nences were a part of the corona was abandoned, and
it was perceived that the two phenomena were to a
great extent independent. At the eclipse of 1868,
which the astronomers, aroused by the wonderful
scene of 1842, and eager to test the powers of the
newly invented spectroscope, flocked to India to
witness, Janssen conceived the idea of employing the
spectroscope to render the prominences visible when
there was no eclipse. He succeeded the very next
day, and these phenomena have been studied in that
way ever since.

There are recognized two kinds of prominences —
the "eruptive" and the "quiescent." The latter,
which are cloud-like in form, may be seen almost any-
where along the edge of the sun; but the former,
7 119

CURIOSITIES OF THE SKY

which often shoot up as if hurled from mighty vol-
canoes, appear to be associated with sun-spots, and
appear only above the zones where spots abound.
Either of them, when seen in projection against the
brilliant solar disk, appears white, not red, as against
a background of sky. The quiescent prominences,
whose elevation is often from forty thousand to sixty
thousand miles, consist, as the spectroscope shows,
mainly of hydrogen and helium. The latter, it will be
remembered, is an element which was known to be in
the sun many years before the discovery that it also
exists in small quantities on the earth. A fact which
may have a significance which we cannot at present
see is that the emanation from radium gradually and
spontaneously changes into helium, an alchemist ical
feat of nature that has opened many curious vistas
to speculative thinkers. The eruptive prominences,
which do not spread horizontally like the others, but
ascend with marvellous velocity to elevations of half
a million miles or more, are apparently composed
largely of metallic vapors — i.e., metals which are
usually solid on the earth, but which at solar tem-
peratures are kept in a volatilized state. The
velocity of their ascent occasionally amounts to
three hundred or four hundred miles per second. It
is known from mathematical considerations that the
gravitation of the sun would not be able to bring back
any body that started from its surface with a velocity
exceeding three hundred and eighty-three miles per
second ; so it is evident that some of the matter hurled
forth in eruptive prominences may escape from
solar control and go speeding out into space, cooling

1 20

A SOLAR "PROMINENCE. PHOTOGRAPHED MAY 21, 1907

1

THE BANNERS OF THE SUN

and condensing into solid masses. There seems to be
no reason why some of the projectiles from the sun
might not reach the planets. Here, then, we have,
on a relatively small scale, explosions recalling those
which it has been imagined may be the originating
cause of some of the sudden phenomena of the stellar
heavens.

Of the sun-spots it is not our intention here specially
to speak, but they evidently have an intimate con-
nection with eruptive prominences, as well as some
relation, not yet fully understood, with the corona.
Of the real cause of sun-spots we know virtually noth-
ing, but recent studies by Professor Hale and others
have revealed a strange state of things in the clouds of
metallic vapors floating above them and their sur-
roundings. Evidences of a cyclonic tendency have
been found, and Professor Hale has proved that sun-
spots are strong magnetic fields, and consist of
columns of ionized vapors rotating in opposite
directions in the two hemispheres. A fact which may
have the greatest significance is that titanium and
vanadium have been found both in sun-spots and
in the remarkable variable Mira Ceti, a star which
every eleven months, or thereabout, flames up with
great brilliancy and then sinks back to invisibility
with the naked eye. It has been suggested that sun-
spots are indications of the beginning of a process in
the sun which will be intensified until it falls into the
state of such a star as Mira. Stars very far advanced
in evolution, without showing variability, also ex-
hibit similar spectra ; so that there is much reason for
regarding sunspots as emblems of advancing age.

123

CURIOSITIES OF THE SKY

The association of the corona with sun-spots is less
evident than that of the eruptive prominences; still
such an association exists, for the form and extent of
the corona vary with the sun-spot period of which we
shall presently speak. The constitution of the corona
remains to be discovered. It is evidently in part
gaseous, but it also probably contains matter in the
form of dust and small meteors. It includes one
substance altogether mysterious — ' ' coronium . ' ' There
are reasons for thinking that this may be the lightest
of all the elements, and Professor Young, its dis-
coverer, said that it was "absolutely unique in nature;
utterly distinct from any other known form of matter,
terrestrial, solar, or cosmical." The enormous ex-
tent of the corona is one of its riddles. Since the
development of the curious subject of the "pressure of
light" it has been proposed to account for the sus-
tentation of the corona by supposing that it is borne
upon the billows of light continually poured out from
the sun. Experiment has proved, what mathemat-
ical considerations had previously pointed out as
probable, that the waves of light exert a pressure or
driving force, which becomes evident in its effects if
the body acted upon is sufficiently small. In that
case the light pressure will prevail over the attraction
of gravitation, and propel the attenuated matter
away from the sun in the teeth of its attraction. The
earth itself would be driven away if, instead of con-
sisting of a solid globe of immense aggregate mass,
it were a cloud of microscopic particles. The reason
is that the pressure varies in proportion to the sur-
face of the body acted upon, while the gravitational

124

THE BANNERS OF THE SUN

attraction is proportional to the volume, or the total
amount of matter in the body. But the surface of
any body depends upon the square of its diameter,
while the volume depends upon the cube of the
diameter. If, for instance, the diameter is represented
by 4, the surface will be proportional to 4 x 4, or 16,
and the volume to 4 x 4 x 4, or 64; but if the diameter
is taken as 2, the surface will be 2 x 2, or 4, and the
volume 2 x 2 x 2, or 8. Now, the ratio of 4 to 8 is
twice as great as that of 16 to 64. If the diameter
is still further decreased, the ratio of the surface to the
volume will proportionally grow larger; in other words,
the pressure will gain upon the attraction, and what-
ever their original ratio may have been, a time will
come, if the diminution of size continues, when the
pressure will become more effective than the attraction,
and the body will be driven away. Supposing the par-
ticles of the corona to be below the critical size for the
attraction of a mass like that of the sun to control
them, they would be driven off into the surrounding
space and appear around the sun like the clouds of dust
around a mill. We shall return to this subject in
connection with the Zodiacal Light, the Aurora, and
Comets.

On the other hand, there are parts of the corona
which suggest by their forms the play of electric or
magnetic forces. This is beautifully shown in some
of the photographs that have been made of the corona
during recent eclipses. Take, for instance, that of the
eclipse of 1900. The sheaves of light emanating from
the poles look precisely like the "lines of force" sur-
rounding the poles of a magnet, It will be noticed

CURIOSITIES OF THE SKY

in this photograph that the corona appears to consist
of two portions: one comprising the polar rays just
spoken of, and the other consisting of the broader,
longer, and less-defined masses of light extending out
from the equatorial and middle-latitude zones. Yet
even in this more diffuse part of the phenomenon one
can detect the presence of submerged curves bearing
more or less resemblance to those about the poles.
Just what part electricity or electro-magnetism plays
in the mechanism of the solar radiation it is im-
possible to say, but on the assumption that it is a very
important part is based the hypothesis that there
exists a direct solar influence not only upon the mag-
netism, but upon the weather of the earth. This hy-
pothesis has been under discussion for half a century,
and still we do not know just how much truth it rep-
resents. It is certain that the outbreak of great dis-
turbances on the sun, accompanied by the formation of
sun-spots and the upshooting of eruptive prominences
(phenomena which we should naturally expect to be
attended by action), have been instantly followed by
corresponding " magnetic storms" on the earth and
brilliant displays of the auroral lights. There have
been occasions when the influence has manifested
itself in the most startling ways, a great solar outburst
being followed by a mysterious gripping of the cable
and telegraph systems of the world, as if an in visible
and irresistible hand had seized them. Messages are
abruptly cut off, sparks leap from the telegraph in-
struments, and the entire earth seems to have been
thrown into a magnetic flurry. These occurrences
affect the mind with a deep impression of the depend-

126

THE BANNERS OF THE SUN

ence of our planet on the sun, such as we do not derive
from the more familiar action of the sunlight on the
growth of plants and other phenomena of life de-
pending on solar influences.

Perhaps the theory of solar magnetic influence upon
the weather is best known in connection with the
"sun-spot cycle." This, at any rate, is, as already
remarked, closely associated with the corona. Its
existence was discovered in 1843 by the German as-
tronomer Schwabe. It is a period of variable length,
averaging about eleven years, during which the num-
ber of spots visible on the sun first increases to a
maximum, then diminishes to a minimum, and finally
increases again to a maximum. For unknown reasons
the period is sometimes two or three years longer than
the average and sometimes as much shorter. Never-
theless, the phenomena always recur in the same order.
Starting, for instance, with a time when the observer
can find few or no spots, they gradually increase in
number and size until a maximum, in both senses, is
reached, during which the spots are often of enormous
size and exceedingly active. After two or three years
they begin to diminish in number, magnitude, and
activity until they almost or quite disappear. A
strange fact is that when a new period opens, the spots
appear first in high northern and southern latitudes,
far from the solar equator, and as the period ad-
vances they not only increase in number and size, but
break out nearer and nearer to the equator, the last
spots of a vanishing period sometimes lingering in the
equatorial region after the advance-guard of its suc-
cessor has made its appearance in the high latitudes.

127

CURIOSITIES OF THE SKY

Spots are never seen on the equator nor near the
poles. It was not very long after the discovery of
the sun-spot cycle that the curious observation was
made that a striking coincidence existed between the
period of the sun-spots and another period affecting
the general magnetic condition of the earth. When a
curved line representing the varying number of sun-
spots was compared with another curve showing the
variations in the magnetic state of the earth the two
were seen to be in almost exact accord, a rise in one
curve corresponding to a rise in the other, and a fall
to a fall. Continued observation has proved that this
is a real coincidence and not an accidental one, so
that the connection, although as yet unexplained, is
accepted as established. But does the influence ex-
tend further, and directly affect the weather and the
seasons as well as the magnetic elements on the earth ?
A final answer to this question cannot yet be given,
for the evidence is contradictory, and the interpreta-
tions put upon it depend largely on the predilections
of the judges.

But, in a broad sense, the sun-spots and the phenom-
ena connected with them must have a relation to
terrestrial meteorology, for they prove the sun to be a
variable star. Reference was made, a few lines above,
to the resemblance of the spectra of sun-spots to
those of certain stars which seem to be failing through
age. This in itself is extremely suggestive ; but if this
resemblance had never been discovered, we should
have been justified in regarding the sun as variable
in its output of energy; and not only variable, but
probably increasingly so. The very inequalities in

128

THE BANNERS OF THE SUN

the sun-spot cycle are suspicious. When the sun is
most spotted its total light may be reduced by one-
thousandth part, although it is by no means certain
that its outgiving of thermal radiations is then re-
duced. A loss of one-thousandth of its luminosity
would correspond to a decrease of .0025 of a stellar
magnitude, considering the sun as a star viewed from
distant space. So slight a change would not be per-
ceptible; but it is not alone sun-spots which obscure
the solar surface, its entire globe is enveloped with an
obscuring veil. When studied with a powerful tele-
scope the sun's surface is seen to be thickly mottled
with relatively obscure specks, so numerous that it
has been estimated that they cut off from one-tenth
to one-twentieth of the light that we should receive
from it if the whole surface were as brilliant as its
brightest parts. The condition of other stars warrants
the conclusion that this obscuring envelope is the prod-
uct of a process of refrigeration which will gradually
make the sun more and more variable until its history
ends in extinction. Looking backward, we see a time
when the sun must have been more brilliant than it is
now. At that time it probably shone with the blind-
ing white splendor of such stars as Sirius, Spica, and
Vega; now it resembles the relatively dull Procyon;
in time it will turn ruddy and fall into the closing
cycle represented by Antares. Considering that once
it must have been more radiantly powerful than at
present, one is tempted to wonder if that could have
been the time when tropical life flourished within the
earth's polar circles, sustained by a vivific energy
in the sun which it has now lost.

129

CURIOSITIES OF THE SKY

The corona, as we have said, varies with the sun-
spot cycle. When the spots are abundant and active the
corona rises strong above the spotted zones, forming
immense beams or streamers, which on one occasion,
at least, had an observed length of ten million miles.
At the time of a spot minimum the corona is less brill-
iant and has a different outline. It is then that the
curved polar rays are most conspicuous. Thus the
vast banners of the sun, shaken out in the eclipse, are
signals to tell of its varying state, but it will probably
be long before we can read correctly their messages.

VIII

THE ZODIACAL LIGHT MYSTERY

HPHERE is a singular phenomenon in the sky — one
1 of the most puzzling of all — which has long
arrested the attention of astronomers, defying their
efforts at explanation, but which probably not one
in a hundred, and possibly not one in a thousand, of
the readers of this book has ever seen. Yet its
name is often spoken, and it is a conspicuous object
if one knows when and where to look for it, and
when well seen it exhibits a mystical beauty which
at the same time charms and awes the beholder. It
is called "The Zodiacal Light," because it lies within
the broad circle of the Zodiac, marking the sun's
apparent annual path through the stars. What it is
nobody has yet been able to find out with certainty,
and books on astronomy usually speak of it with
singular reserve. But it has given rise to many
remarkable theories, and a true explanation of it
would probably throw light on a great many other
celestial mysteries. The Milky Way is a more won-
derful object to look upon, but its nature can be com-
prehended, while there is a sort of uncanniness about
the Zodiacal Light which immediately impresses one
upon seeing it, for its part in the great scheme of
extra-terrestrial affairs is not evident.

CURIOSITIES OF THE SKY

If you are out-of-doors soon after sunset — say, on an
evening late in the month of February — you may per-
ceive, just after the angry flush of the dying winter's
day has faded from the sky, a pale ghostly presence
rising above the place where the sun went down.
The writer remembers from boyhood the first time it
was pointed out to him and the unearthly impression
that it made, so that he afterward avoided being out
alone at night, fearful of seeing the spectral thing
again. The phenomenon brightens slowly with the
fading of the twilight, and soon distinctly assumes
the shape of an elongated pyramid of pearly light,
leaning toward the south if the place of observation
is in the northern hemisphere. It does not impress the
observer at all in the same manner as the Milky Way;
that looks far off and is clearly among the stars, but
the Zodiacal Light seems closer at hand, as if it were
something more intimately concerning the earth. To
all it immediately suggests a connection, also, with
the sunken sun. If the night is clear and the moon
absent (and if you are in the country, for city lights
ruin the spectacles of the sky), you will be able to
watch the apparition for a long time. You will
observe that the Light is brightest near the horizon,
gradually fading as the pyramidal beam mounts
higher, but in favorable circumstances it may be
traced nearly to the meridian south of the zenith,
where its apex at last vanishes in the starlight. It
continues visible during the evenings of March and
part of April, after which, ordinarily, it is seen no
more, or if seen is relatively faint and unimpressive.
But when autumn comes it appears again, this time

132

THE ZODIACAL LIGHT MYSTERY

not like a wraith hovering above the westward tomb of
the day-god, but rather like a spirit of the morning
announcing his reincarnation in the east.

The reason why the Zodiacal Light is best seen in
our latitudes at the periods just mentioned is because
at those times the Zodiac is more nearly perpendicular
to the horizon, first in the west and then in the east;
and, since the phenomenon is confined within the
borders of the Zodiac, it cannot be favorably placed
for observation when the zodiacal plane is but slightly
inclined to the horizon. Its faint light requires the
contrast of a background of dark sky in order to be
readily perceptible. But within the tropics, where
the Zodiac is always at a favorable angle, the mys-
terious light is more constantly visible. Nearly all
observant travellers in the equatorial regions have
taken particular note of this phenomenon, for being
so much more conspicuous there than in the temperate
zones it at once catches the eye and holds the atten-
tion as a novelty. Humboldt mentions it many times
in his works, for his genius was always attracted by
things out of the ordinary and difficult of explana-
tion, and he made many careful observations on its
shape, its brilliancy, and its variations; for there can
be no doubt that it does vary, and sometimes to an
astonishing degree. It is said that it once remained
practically invisible in Europe for several years in
succession. During a trip to South Africa in 1909 an
English astronomer, Mr. E. W. Maunder, found a
remarkable difference between the appearance of the
Zodiacal Light on his going and coming voyages.
In fact, when crossing the equator going south he did

CURIOSITIES OF THE SKY

not see it at all; but on returning he had, on March
6th, when one degree south of the equator, a memora-
ble view of it. "It was a bright, clear night, and the
Zodiacal Light was extraordinarily brilliant — brighter
than he had ever seen it before. The Milky Way
was not to be compared with it. The brightest part
extended to 75° from the sun. There was a faint
and much narrower extension which they could just
make out beyond the Pleiades along the ecliptic, but
the greater part of the Zodiacal Light showed as a
broad truncated column, and it did not appear nearly
as conical as he had before seen it."

When out of the brief twilight of intertropical
lands, where the sun drops vertically to the horizon
and night rushes on like a wave of darkness, the
Zodiacal Light shoots to the very zenith, its color is
described as a golden tint, entirely different from the
silvery sheen of the Milky Way. If I may venture
again to refer to personal experiences and impressions,
I will recall a view of the Zodiacal Light from the
summit of the cone of Mt. Etna in the autumn of
the year 1896 (more briefly described in Astronomy
with the Naked Eye). There are few lofty mountains
so favorably placed as Etna for observations of this
kind. It was once resorted to by Prof. George E.
Hale, in an attempt to see the solar corona without an
eclipse. Rising directly from sea-level to an elevation
of nearly eleven thousand feet, the observer on its
summit at night finds himself, as it were, lost in the
midst of the sky. But for the black flanks of the
great cone on which he stands he might fancy himself
to be in a balloon. On the occasion to which I refer

THE ZODIACAL LIGHT MYSTERY

the world beneath was virtually invisible in the
moonless night. The blaze of the constellations over-
head was astonishingly brilliant, yet amid all their
magnificence my attention was immediately drawn
to a great tapering light that sprang from the place
on the horizon where the sun would rise later, and
that seemed to be blown out over the stars like a long,
luminous veil. It was the finest view of the Zodiacal
Light that I had ever enjoyed — thrilling in its strange-
ness— but I was almost disheartened by the indif-
ference of my guide, to whom it was only a light and
nothing more. If he had no science, he had less
poetry — rather a remarkable thing, I thought, for a
child of his clime. The Light appeared to me to be
distinctly brighter than the visible part of the Milky
Way which included the brilliant stretches in Auriga
and Perseus, and its color, if one may speak of color
in connection with such an object, seemed richer than
that of the galactic band ; but I did not think of it as
yellow, although Humboldt has described it as re-
sembling a golden curtain drawn over the stars, and
Du Chaillu in Equatorial Africa found it of a bright
yellow color. It may vary in color as in con-
spicuousness. The fascination of that extraordinary
sight has never faded from my memory. I turned to
regard it again and again, although I had never seen
the stellar heavens so brilliant, and it was one of the
last things I looked for when the morning glow began
softly to mount in the east, and Sicily and the Medi-
terranean slowly emerged from the profound shadow
beneath us.
The Zodiacal Light seems never to have attracted

CURIOSITIES OF THE SKY

from astronomers in general the amount of careful
attention that it deserves; perhaps because so little
can really be made of it as far as explanation is con-
cerned. I have referred to the restraint that scientific
writers apparently feel in speaking of it. The grounds
for speculation that it affords may be too scanty to
lead to long discussions, yet it piques curiosity, and
as we shall see in a moment has finally led to a most
interesting theory. Once it was the subject of an
elaborate series of studies which carried the observer
all round the world. That was in 1845-46, during
the United States Exploring Expedition that visited
the then little known Japan. The chaplain of the
fleet, the Rev. Mr. Jones, went out prepared to study
the mysterious light in all its phases. He saw it from
many latitudes on both sides of the equator, and the
imagination cannot but follow him with keen interest
in his world-circling tour, keeping his eyes every
night fixed upon the phantasm overhead, whose
position shifted with that of the hidden sun. He
demonstrated that the glow extends at times com-
pletely across the celestial dome, although it is rel-
atively very faint directly behind the earth. On his
return the government published a large volume of his
observations, in which he undertook to show that the
phenomenon was due to the reflection of sunlight from
a ring of meteoric bodies encircling the earth. But,
after all, this elaborate investigation settled nothing.
Prof. E. E. Barnard has more recently devoted
much attention to the Zodiacal Light, as well as to a
strange attendant phenomenon called the "Gegen-
schein," or Counterglow, because it always appears at

136

THE ZODIACAL LIGHT MYSTERY

that point in the sky which is exactly opposite to the
sun. The Gegenschein is an extremely elusive
phenomenon, suitable only for eyes that have been
specially trained to see it. Professor Newcomb has
cautiously remarked that "it is said that in that point
of the heavens directly opposite to the sun there is
an elliptical patch of light. . . . This phenomenon is so
difficult to account for that its existence is sometimes
doubted; yet the testimony in its favor is difficult to
set aside." It certainly cannot be set aside at all
since the observations of Barnard. I recall an at-
tempt to see it under his guidance during a visit to
Mount Hamilton, when he was occupied there with the
Lick telescope. Of course, both the Gegenschein and
the Zodiacal Light are too diffuse to be studied with
telescopes, which, so to speak, magnify them out of
existence. They can only be successfully studied
with the naked eye, since every faintest glimmer that
they afford must be utilized. This is especially true
of the Gegenschein. At Mount Hamilton, Mr. Barnard
pointed out to me its location with reference to cer-
tain stars, but with all my gazing I could not be sure
that I saw it. To him, on the contrary, it was obvious;
he had studied it for months, and was able to indicate
its shape, its boundaries, its diameter, and the dec-
lination of its centre with regard to the ecliptic.
There is not, of course, the shadow of a doubt of the
existence of the Gegenschein, and yet I question if one
person in a million has ever seen or ever will see it.
The Zodiacal Light,on the other hand, is plain enough,
provided that the time and the circumstances of the
observation are properly chosen.

CURIOSITIES OF THE SKY

In the attempts to explain the Zodiacal Light, the
favorite hypothesis has been that it is an appendage
of the sun — perhaps simply an extension of the corona
in the plane of the ecliptic, which is not very far from
coinciding with that of the sun's equator. This idea
is quite a natural one, because of the evident relation
of the light to the position of the sun. The vast ex-
tension of the equatorial wings of the corona in 1878
gave apparent support to this hypothesis ; if the sub-
stance of the corona could extend ten million miles
from the sun, why might it not extend even one
hundred million, gradually fading out beyond the
orbit of the earth? A variation of this hypothesis
assumes that the reflection is due to swarms of meteors
circling about the sun, in the plane of its equator, all
the way from its immediate neighborhood to a distance
exceeding that of the earth. But in neither form is
the hypothesis satisfactory; there is nothing in the
appearance of the corona to indicate that it extends
even as far as the planet Mercury, while as to meteors,
the orbits of the known swarms do not accord with
the hypothesis, and we have no reason to believe that
clouds of others exist travelling in the part of space
where they would have to be in order to answer the
requirements of the theory. The extension of the
corona in 1878 did not resemble in its texture the
Zodiacal Light.

Now, it has so often happened in the history of
science that an important discovery in one branch
has thrown unexpected but most welcome light upon
some pending problem in some other branch, that a
strong argument might be based upon that fact alone

138

THE ZODIACAL LIGHT MYSTERY

against the too exclusive devotion of many investi-
gators to the narrow lines of their own particular
specialty; and the Zodiacal Light affords a case in
point, when it is considered in connection with recent
discoveries in chemistry and physics. From the fact
that atoms are compound bodies made up of corpuscles
at least a thousand times smaller than the smallest
known atom — a fact which astounded most men of
science when it was announced a few years ago —
a new hypothesis has been developed concerning the
nature of the Zodiacal Light (as well as other as-
tronomical riddles), and this hypothesis comes not
from an astronomer, but from a chemist and physicist,
the Swede, Svante Arrhenius. In considering an
outline of this new hypothesis we need neither accept
nor reject it; it is a case rather for suspension of
judgment.

To begin with, it carries us back to the "pressure
of light" mentioned in the preceding chapter. The
manner in which this pressure is believed generally
to act was there sufficiently explained, and it only
remains to see how it is theoretically extended to the
particles of matter supposed to constitute the Zodiacal
Light. We know that corpuscles, or "fragments of
atoms" negatively electrified, are discharged from
hot bodies. Streams of these "ions" pour from
many flames and from molten metals; and the im-
pact of the cathode and ultra-violet rays causes them
to gush even from cold bodies. In the vast labora-
tory of the sun it is but reasonable to suppose that
similar processes are taking place. "As a very hot
metal emits these corpuscles," says Prof. J. J. Thom-

CURIOSITIES OF THE SKY

son, "it does not seem an improbable hypothesis that
they are emitted by that very hot body, the sun."
Let it be assumed, then, that the sun does emit them ;
what happens next? Negatively charged corpuscles,
it is known, serve as nuclei to which particles of matter
in the ordinary state are attracted, and it is probable
that those emitted from the sun immediately pick up
loads in this manner and so grow in bulk. If they
grow large enough the gravitation of the sun draws
them back, and they produce a negative charge in the
solar atmosphere. But it is probable that many
of the particles do not attain the critical size which,
according to the principles before explained, would
enable the gravitation of the sun to retain them in
opposition to the pressure of the waves of light, and
with these particles the light pressure is dominant.
Clouds of them may be supposed to be continually
swept away from the sun into surrounding space,
moving mostly in or near the plane of the solar equa-
tor, where the greatest activity, as indicated by sun-
spots and related phenomena, is taking place. As
they pass outward into space many of them en-
counter the earth. If the earth, like the moon, had
no atmosphere the particles would impinge directly on
its surface, giving it a negative electric charge. But
the presence of the atmosphere changes all that, for
the first of the flying particles that encounter it im-
part to it their negative electricity, and then, since
like electric charges repel like, the storm of particles
following will be sheered off from the earth, and will
stream around it in a maze of hyperbolic paths.
Those that continue on into space beyond the earth

140

THE ZODIACAL LIGHT MYSTERY

may be expected to continue picking up wandering
particles of matter until their bulk has become so
great that the solar attraction prevails again over the
light pressure acting upon them, and they turn again
sunward. Passing the earth on their return they
will increase the amount of dust-clouds careering round
it; and these will be further increased by the action
of the ultra-violet rays of the sunlight causing par-
ticles to shoot radially away from the earth when the
negative charge of the upper atmosphere has reached
a certain amount, which particles, although starting
sunward, will be swept back to the earth with the on-
coming streams. As the final result of all this ac-
cumulation of flying and gyrating particles in the
earth's neighborhood, we are told that the latter must
be transformed into the semblance of a gigantic solid-
headed comet provided with streaming tails, the
longest of them stretching away from the direction
of the sun, while another shorter one extends toward
the sun. This shorter tail is due to the particles that
we have just spoken of as being driven sunward from
the earth by the action of ultra-violet light. No
doubt this whole subject is too technical for popular
statement; but at any rate the general reader can
understand the picturesque side of the theory, for
its advocates assure us that if we were on the moon
we should doubtless be able to see the comet-like tails
of the earth, and then we could appreciate the part
that they play in producing the phenomenon of the
Zodiacal Light.

That the Light as we see it could be produced by
the reflection of sunlight from swarms of particles

141

CURIOSITIES OF THE SKY

careering round the earth in the manner supposed by
Arrhenius' hypothesis is evident enough; and it will
be observed that the new theory, after all, is only an-
other variant of the older one which attributes the
Zodiacal Light to an extension of the solar corona.
But it differs from the older theory in affording an
explanation of the manner in which the extension is
effected, and it differentiates between the corona
proper and the streams of negative particles shot
away from the sun. In its details the hypothesis of
Arrhenius alsp affords an explanation of many
peculiarities of the Zodiacal Light, such as that it is
confined to the neighborhood of the ecliptic, and that
it is stronger on the side of the earth which is just
turning away from a position under the sun than on
the other side; but it would carry us beyond our
limits to go into these particulars. The Gegenschein,
according to this theory, is a part of the same phenom-
enon as the Zodiacal Light, for by the laws of
perspective it is evident that the reflection from the
streams of particles situated at a point directly op-
posite to the sun would be at a maximum, and this
is the place which the Gegenschein occupies. Apart
from its geometrical relations to the position of the
sun, the variability of the Zodiacal Light appears to
affirm its solar dependence, and this too would be
accounted for by Arrhenius* hypothesis better than
by the old theory of coronal extension. The amount
of corpuscular discharge from the sun must nat-
urally be governed by the state of relative activity
or inactivity of the latter, and this could not but be
reflected in the varying splendor of the Zodiacal

142

THE ZODIACAL LIGHT MYSTERY

Light. But much more extended study than has
yet been given to the subject will be required before
we can feel that we know with reasonable certainty
what this mysterious phenomenon really is. By the
hypothesis of Arrhenius every planet that has an
atmosphere must have a Zodiacal Light attending it,
but the phenomenon is too faint for us to be able to
see it in the case, for instance, of Venus, whose at-
mosphere is very abundant. The moon has no
corresponding "comet's tail" because, as already ex-
plained, of the lack of a lunar atmosphere to repel the
streams by becoming itself electrified; but if there
were a lunar Zodiacal Light, no doubt we could see it
because of the relative nearness of our satellite.

IX

MARVELS OF THE AURORA

ONE of the most vivid recollections of my early
boyhood is that of seeing my father return
hastily into the house one evening and call out to the
family: "Come outside and look at the sky!" Ours
was a country house situated on a commanding site,
and as we all emerged from the doorway we were
dumfounded to see the heavens filled with pale flames
which ran licking and quivering over the stars. In-
stantly there sprang into my terrified mind the
recollection of an awful description of "the Day of
Judgment'* (the Dies Ircz), which I had heard with
much perturbation of spirit in the Dutch Reformed
church from the lips of a tall, dark-browed, dread fully-
in-earnest preacher of the old-fashioned type. My
heart literally sank at sight of the spectacle, for it
recalled the preacher's very words; it was just as he
had said it would be, and it needed the assured
bearing of my elders finally to convince me that

"That Day of Wrath, O dreadful day,
When Heaven and Earth shall pass away,
As David and the Sibyl say,"

had not actually come upon us. And even the older
members of the household were not untouched with

144

• '••'''Sir

•si*

MARVELS OF THE AURORA

misgivings when menacing spots of crimson appeared,
breaking out now here, now there, in the shuddering
sky. Toward the north the spectacle was appalling.
A huge arch spanned an unnaturally dark segment
resting on the horizon, and above this arch sprang up
beams and streamers in a state of incessant agitation,
sometimes shooting up to the zenith with a velocity
that took one's breath, and sometimes suddenly fall-
ing into long ranks, and marching, marching, marching,
like an endless phalanx of fiery spectres, and moving,
as I remember, always from east to west. The ab-
solute silence with which these mysterious evolutions
were performed and the quavering reflections which
were thrown upon the ground increased the awfulness
of the exhibition. Occasionally enormous curtains
of lambent flame rolled and unrolled with a majestic
motion, or were shaken to and fro as if by a mighty,
noiseless wind. At times, too, a sudden billowing
rush would be made toward the zenith, and for a
minute the sky overhead would glow so brightly that
the stars seemed to have been consumed. The spec-
tacle continued with varying intensity for hours.

This exhibition occurred in Central New York,
a latitude in which the Aurora Borealis is seldom seen
with so much splendor. I remember another similar
one seen from the city of New York in November,
1882. On this last occasion some observers saw a
great upright beam of light which majestically moved
across the heavens, stalking like an apparition in the
midst of the auroral pageant, of whose general move-
ments it seemed to be independent, maintaining always
its upright posture, and following a magnetic parallel

J47

CURIOSITIES OF THE SKY

from east to west. This mysterious beam was seen
by no less than twenty-six observers in different parts
of the country, and a comparison of their observations
led to a curious calculation indicating that the
apparition was about one hundred and thirty -three
miles tall and moved at the speed of ten miles per
second!

But, as everybody knows, it is in the Arctic regions
that the Aurora, or the "Northern Lights/' can best
be seen. There, in the long polar night, when for
months together the sun does not rise, the strange
coruscations in the sky often afford a kind of spectral
daylight in unison with the weird scenery of the
world of ice. The pages in the narratives of Arctic
exploration that are devoted to descriptions of the
wonderful effects of the Northern Lights are second
to none that man has ever penned in their fascination.
The lights, as I have already intimated, display as-
tonishing colors, particularly shades of red and green,
as they flit from place to place in the sky. The dis-
covery that the magnetic needle is affected by the
Aurora, quivering and darting about in a state of
extraordinary excitement when the lights are play-
ing in the sky, only added to the mystery of the
phenomenon until its electro-magnetic nature had
been established. This became evident as soon as
it was known that the focus of the displays was the
magnetic pole; and when the far South was visited
the Aurora Australis was found, having its centre at
the South Magnetic Pole. Then, if not before, it was
clear that the earth was a great globular magnet,
having its poles of opposite magnetism, and that

148

MARVELS OF THE AURORA

the auroral lights, whatever their precise cause might
be, were manifestations of the magnetic activity of our
planet. After the invention of magnetic telegraphy
it was found that whenever a great Aurora occurred
the telegraph lines were interrupted in their opera-
tion, and the ocean cables ceased to work. Such a
phenomenon is called a "magnetic storm."

The interest excited by the Aurora in scientific
circles was greatly stimulated when, in the last half
of the nineteenth century, it was discovered that it is
a phenomenon intimately associated with disturb-
ances on the sun. The ancient "Zurich Chronicles,"
extending from the year 1000 to the year 1800, in
which both sun-spots visible to the naked eye and
great displays of the auroral lights were recorded,
first set Rudolph Wolf on the track of this discovery.
The first notable proof of the suspected connection
was furnished with dramatic emphasis by an oc-
currence which happened on September i, 1859.
Near noon on that day two intensely brilliant points
suddenly broke out in a group of sun-spots which were
under observation by Mr. R. C. Carrington at his
observatory at Redhill, England. The points re-
mained visible for not more than five minutes, during
which interval they moved thirty-five thousand miles
across the solar disk. Mr. R. Hodgson happened to
see the same phenomenon at his observatory at
Highgate, and thus all possibility of deception was
removed. But neither of the startled observers could
have anticipated what was to follow, and, indeed, it
was an occurrence which has never been precisely
duplicated. I quote the eloquent account given by

CURIOSITIES OF THE SKY

Miss Clerke, in her History of Astronomy During the
Nineteenth Century.

"This unique phenomenon seemed as if specially
designed to accentuate the inference of a sympathetic
relation between the earth and the sun. From August
28 to September 4, 1859, a magnetic storm of un-
paralleled intensity, extent, and duration was in
progress over the entire globe. Telegraphic com-
munication was everywhere interrupted — except, in-
deed, that it was in some cases found practicable to
work the lines without batteries by the agency of the
earth-currents alone; sparks issued from the wires;
gorgeous auroras draped the skies in solemn crimson
over both hemispheres, and even in the tropics; the
magnetic needle lost all trace of continuity in its
movements and darted to and fro as if stricken with
inexplicable panic. The coincidence was even closer.
At the very instant of the solar outburst witnessed by
Carrington and Hodgson the photographic apparatus
at Kew registered a marked disturbance of all the
three magnetic elements; while shortly after the en-
suing midnight the electric agitation culminated,
thrilling the whole earth with subtle vibrations, and
lighting up the atmosphere from pole to pole with
coruscating splendors which perhaps dimly recall the
times when our ancient planet itself shone as a star."

If this amazing occurrence stood alone, and as I
have already said it has never been exactly duplicated,
doubt might be felt concerning some of the inferences
drawn from it; but in varying forms it has been re-
peated many times, so that now hardly any one ques-
tions the reality of the assumed connection between

MARVELS OF THE AURORA

solar outbursts and magnetic storms accompanied by
auroral displays on the earth. It is true that the late
Lord Kelvin raised difficulties in the way of the hy-
pothesis of a direct magnetic action of the sun upon
the earth, because it seemed to him that an inadmissi-
ble quantity of energy was demanded to account for
such action. But no calculation like that which he
made is final, since all calculations depend upon the
validity of the data ; and no authority is unshakable in
science, because no man can possess omniscience. It
was Lord Kelvin who, but a few years before the
thing was actually accomplished, declared that aerial
navigation was an impracticable dream, and demon-
strated its impracticability by calculation. However
the connection may be brought about, it is as certain
as evidence can make it that solar outbursts are coin-
cident with terrestrial magnetic disturbances, and
coincident in such a way as to make the inference of a
causal connection irresistible. The sun is only a little
more than a hundred times its own diameter away
from the earth. Why, then, with the subtle connection
between them afforded by the ether which conveys
to us the blinding solar light and the life-sustaining
solar heat, should it be so difficult to believe that the
sun's enormous electric energies find a way to us also ?
No doubt the impulse coming from the sun acts upon
the earth after the manner of a touch upon a trigger,
releasing energies which are already stored up in our
planet.

But besides the evidence afforded by such occur-
rences as have been related of an intimate connection
between solar outbreaks and terrestrial magnetic

CURIOSITIES OF THE SKY

flurries, attended by magnificent auroral displays,
there is another line of proof pointing in the same
direction. Thus, it is known that the sun-spot period,
as remarked in a preceding chapter, coincides in a
most remarkable manner with the periodic fluctua-
tions in the magnetic state of the earth. This coin-
cidence runs into the most astonishing details. For
instance, when the sun-spot period shortens, the
auroral period shortens to precisely the same extent;
as the short sun-spot periods usually bring the most in-
tense outbreaks of solar activity, so the corresponding
short auroral periods are attended by the most violent
magnetic storms; a secular period of about two
hundred and twenty-two years affecting sun-spots is
said to have its auroral duplicate; a shorter period of
fifty-five and a half years, which some observers be-
lieve that they have discovered appears also to be com-
mon to the two phenomena; and yet another "super-
posed" period of about thirty-five years, which some
investigators aver exists, affects sun-spots and auroras
alike. In short, the coincidences are so numerous
and significant that one would have to throw the
doctrine of probability to the winds in order to be
able to reject the conclusion to which they so plainly
lead.

But still the question recurs: How is the influence
transmitted ? Here Arrhenius comes once more with
his hypothesis of negative corpuscles, or ions, driven
away from the sun by light-pressure — a hypothesis
which seems to explain so many things — and offers
it also as an explanation of the way in which the sun
creates the Aurora. He would give the Aurora the

MARVELS OF THE AURORA

same lineage with the Zodiacal Light. To under-
stand the application of this theory we must first
recall the fact that the earth is a great magnet having
its two opposite poles of magnetism, one near the
Arctic and the other near the Antarctic Circle. Like
all magnets, the earth is surrounded with "lines of
force," which, after the manner of the curved rays we
saw in the photograph of a solar eclipse, start from
a pole, rising at first nearly vertically, then bend
gradually over, passing high above the equator, and
finally descending in converging sheaves to the
opposite pole. Now the axis of the earth is so
placed in space that it lies at nearly a right angle to
the direction of the sun, and as the streams of nega-
tively charged particles come pouring on from the
sun (see the last preceding chapter), they arrive in
the greatest numbers over the earth's equatorial
regions. There they encounter the lines of magnetic
force at the place where the latter have their greatest
elevation above the earth, and where their direction
is horizontal to the earth's surface. Obeying a law
which has been demonstrated in the laboratory, the
particles then follow the lines of force toward the
poles. While they are above the equatorial regions
they do not become luminescent, because at the great
elevation that they there occupy there is virtually
no atmosphere ; but as they pass on toward the north
and the south they begin to descend with the lines of
force, curving down to meet at the poles; and, en-
countering a part of the atmosphere comparable in
density with what remains in an exhausted Crookes
tube, they produce a glow of cathode rays. This glow

CURIOSITIES OF THE SKY

is conceived to represent the Aurora, which may
consequently be likened to a gigantic exhibition of
vacuum-tube lights. Anybody who recalls his student
days in the college laboratory and who has witnessed
a display of Northern Lights will at once recognize
the resemblance between them in colors, forms, and
behavior. This resemblance had often been noted
before Arrhenius elaborated his hypothesis.

Without intending to treat his interesting theory
as more than a possibly correct explanation of the
phenomena of the Aurora, we may call attention to
some apparently confirmatory facts. One of the
most striking of these relates to a seasonal variation
in the average number of aurorse. It has been ob-
served that there are more in March and September
than at any other time of the year, and fewer in June
and December; moreover (and this is a delicate test
as applied to the theory), they are slightly rarer in
June than in December. Now all these facts seem
to find a ready explanation in the hypothesis of Ar-
rhenius, thus: (i) The particles issuing from the sun
are supposed to come principally from the regions
whose excitement is indicated by the presence of
sun-spots (which accords with Hale's observation that
sun-spots are columns of ionized vapors), and these
regions have a definite location on either side of the
solar equator, seldom approaching it nearer than
within 5° or 10° north or south, and never extending
much beyond 35° toward either pole; (2) The equator
of the sun is inclined about 7° to the plane of the
earth's orbit, from which it results that twice in a
year — viz., in June and December — the earth is directly

158

MARVELS OF THE AURORA

over the solar equator, and twice a year — viz., in
March and September — when it is farthest north or
south of the solar equator, it is over the inner edge
of the sun-spot belts. Since the corpuscles must be
supposed to be propelled radially from the sun, few
will reach the earth when the latter is over the solar
equator in June and December, but when it is over,
or nearly over, the spot belts, in March and September,
it will be in the line of fire of the more active parts
of the solar surface, and relatively rich streams of
particles will reach it. This, as will be seen from
what has been said above, is in strict accord with the
observed variations in the frequency of auroras.
Even the fact that somewhat fewer auroras are seen
in June than in December also finds its explanation
in the known fact that the earth is about three million
miles nearer the sun in the winter than in the summer,
and the number of particles reaching it will vary,
like the intensity of light, inversely as the square of
the distance. These coincidences are certainly very
striking, and they have a cumulative force. If we
accept the theory, it would appear that we ought to
congratulate ourselves that the inclination of the
sun's equator is so slight, for as things stand the
earth is never directly over the most active regions
of the sun-spots, and consequently never suffers from
the maximum bombardment of charged particles of
which the sun is capable. Incessant auroral dis-
plays, with their undulating draperies, flitting colors,
and marching columns might not be objectionable
from the point of view of picturesqueness, but one
magnetic storm of extreme intensity following closely
9 159

CURIOSITIES OF THE SKY

upon the heels of another, for months on end, crazing
the magnetic needle and continually putting the
telegraph and cable lines out of commission, to say
nothing of their effect upon " wireless telegraphy,"
would hardly add to the charms of terrestrial exist-
ence.

One or two other curious points in connection with
Arrhenius' hypothesis may be mentioned. First,
the number of auroras, according to his explanation,
ought to be greatest in the daytime, when the face
of the earth on the sunward side is directly exposed
to the atomic bombardment. Of course visual ob-
servation can give us no information about this, since
the light of the Aurora is never sufficiently intense to
be visible in the presence of daylight, but the records
of the magnetic observatories can be, and have been,
appealed to for information, and they indicate that
the facts actually accord with the theory. Behind
the veil of sunlight in the middle of the afternoon,
there is good reason to believe, auroral exhibitions
often take place which would eclipse in magnificence
those seen at night if we could behold them. Ob-
servation shows, too, that auroras are more frequent
before than after midnight, which is just what we
should expect if they originate in the way that
Arrhenius supposes. Second, the theory offers an ex-
planation of the alleged fact that the formation of
clouds in the upper air is more frequent in years when
aurorae are most abundant, because clouds are the
result of the condensation of moisture upon floating
particles in the atmosphere (in an absolutely dustless
atmosphere there would be no clouds), and it has been

1 60

MARVELS OF THE AURORA

proved that negative ions like those supposed to come
from the sun play a master part in the phenomena of
cloud formation.

Yet another singular fact, almost mystical in its
suggestions, may be mentioned. It seems that the
dance of the auroral lights occurs most frequently
during the absence of the moon from the hemisphere
in which they appear, and that they flee, in greater
part, to the opposite hemisphere when the moon's
revolution in an orbit considerably inclined to the
earth's equator brings her into that where they have
been performing. Arrhenius himself discovered this
curious relation of auroral frequency to the position
of the moon north or south of the equator, and he
explains it in this way: The moon, like the earth, is
exposed to the influx of the ions from the sun; but
having no atmosphere, or almost none, to interfere
with them, they descend directly upon her surface
and charge her with an electric negative potential to a
very high degree. In consequence of this she affects
the electric state of the upper parts of the earth's
atmosphere where they lie most directly beneath her,
and thus prevents, to a large extent, the negative
discharges to which the appearance of the Aurora is
due. And so "the extravagant and erring spirit"
of the Aurora avoids the moon as Hamlet's ghost
fled at the voice of the cock announcing the awakening
of the god of day.

There are even other apparent confirmations
of the hypothesis, but we need not go into them.
We shall, however, find one more application of it
in the next chapter, for it appears to be a kind of cure-

163

CURIOSITIES OF THE SKY

all for astronomical troubles; at any rate, it offers
a conceivable solution of the question, How does
the sun manage to transmit its electric influence to
the earth ? And this solution is so grandiose in con-
ception, and so novel in the mental pictures that it
offers, that its acceptance would not in the least de-
tract from the impression that the Aurora makes
upon the imagination.

STRANGE ADVENTURES OP COMETS

THE fears and legends of ancient times before
Science was born, and the superstitions of the
Dark Ages, sedulously cultivated for theological pur-
poses by monks and priests, have so colored our ideas
of the influence that comets have had upon the
human mind that many readers may be surprised to
learn that it was the apparition of a wonderful comet,
that of 1843, which led to the foundation of our
greatest astronomical institution, the Harvard College
Observatory. No doubt the comet superstition exist-
ed half a century ago, as, indeed, it exists yet to-day,
but in this case the marvellous spectacle in the sky
proved less effective in inspiring terror than in awaken-
ing a desire for knowledge. Even in the sixteenth
century the views that enlightened minds took of
comets tended powerfully to inspire popular con-
fidence in science, and Halley's prediction, after seeing
and studying the motion of the comet which ap-
peared in 1682, that it would prove to be a regular
member of the sun's family and would be seen re-
turning after a period of about seventy-six years, to-
gether with the fulfilment of that prediction, pro-
duced a revulsion from the superstitious notions
which had so long prevailed.

165

CURIOSITIES OF THE SKY

Then the facts were made plain that comets are
subject to the law of gravitation equally with the
planets; that there are many which regularly return
to the neighborhood of the sun (perihelion) ; and that
these travel in orbits differing from those of the
planets only in their greater eccentricity, alt ough
they have the peculiarity that they do not, like the
planets, all go round the sun in the same direction,
and do not keep within the general plane of the
planetary system, but traverse it sometimes from
above and sometimes from below. Other comets,
including most of the " great " ones, appear to travel
in parabolic or, in a few cases, hyperbolic orbits,
which, not being closed curves, never bring them back
again. But it is not certain that these orbits may not
be extremely eccentric ellipses, and that after the
lapse of hundreds, or thousands, of years the comets
that follow them may not reappear. The question
is an interesting one, because if all orbits are really
ellipses, then all comets must be permanent members
of the solar system, while in the contrary case many
of them are simply visitors, seen once and never to
be seen again. The hypothesis that comets are
originally interlopers might seem to derive some
support from the fact that the certainly periodic ones
are associated, in groups, with the great outer planets,
whose attraction appears to have served as a trap
for them by turning them into elliptical orbits and
thus making them prisoners in the solar system.
Jupiter, owing to his great mass and his commanding
situation in the system, is the chief "comet-catcher";
but he catches them not for himself, but for the sun.

1 66

SWIFT'S COMET. TAKEN AT AREQUIPA, MARCH 30, 1892

STRANGE ADVENTURES OF COMETS

Yet if comets do come originally from without the
borders of the planetary system, it does not, by any
means, follow that they were wanderers at large in
space before they yielded to the overmastering at-
traction of the sun. Investigation of the known
cometary orbits, combined with theoretical con-
siderations, has led some astronomers to the con-
clusion that as the sun travels onward through space
he ' ' picks up en route ' ' cometary masses which, with-
out belonging strictly to his empire, are borne along
in the same vast "cosmical current" that carries the
solar system.

But while no intelligent person any longer thinks
that the appearance of a great comet is a token from
the heavenly powers of the approaching death of a
mighty ruler, or the outbreak of a devastating war,
or the infliction of a terrible plague upon wicked man-
kind, science itself has discovered mysteries about
comets which are not less fascinating because they are
more intellectual than the irrational fancies that they
have displaced. To bring the subject properly be-
fore the mind, let us see what the principal phenomena
connected with a comet are.

At the present day comets are ordinarily "picked
up" with the telescope or the photographic plate be-
fore any one except their discoverer is aware of their
existence, and usually they remain so insignificant
in appearance that only astronomers ever see them.
Yet so great is the prestige of the word "comet"
that the discovery of one of these inconspicuous wan-
derers, and its subsequent movements, become items
of the day's news which everybody reads with the

169

CURIOSITIES OF THE SKY

feeling, perhaps, that at least he knows what is going
on in the universe even if he doesn't understand it.
But a truly great comet presents quite a different prop-
osition. It, too, is apt to be detected coming out of
the depths of space before the world at large can get
a glimpse of it, but as it approaches the sun its aspect
undergoes a marvellous change. Agitated apparently
by solar influence, it throws out a long streaming tail
of nebulous light, directed away from the sun and
looking as if blown out like a pennon by a powerful
wind. Whatever may be the position of the comet
with regard to the sun, as it circles round him it con-
tinually keeps its tail on the off side. This, as we shall
soon see, is a fact of capital importance in relation to
the probable nature of comets' tails. Almost at the
same time that the formation of the tail is observed
a remarkable change takes place in the comet's head,
which, by the way, is invariably and not merely
occasionally its most important part. On approach-
ing the sun the head usually contracts. Coincidently
with this contraction a nucleus generally makes its
appearance. This is a bright, star-like point in the
head, and it probably represents the totality of solid
matter that the comet possesses. But it is regarded
as extremely unlikely that even the nucleus consists
of a uniformly solid mass. If it were such, comets
would be far more formidable visitors when they pass
near the planets than they have 'been found to be.
The diameter of the nucleus may vary from a few
hundred up to several thousand miles; the heads, on
the average, are from twenty-five thousand to one
hundred thousand miles in diameter, although a few

170

STRANGE ADVENTURES OF COMETS

have greatly exceeded these dimensions; that of the
comet of 1811, one of the most stupendous ever seen,
was a million and a quarter miles in diameter ! As to
the tails, notwithstanding their enormous length —
some have been more than a hundred million miles
long — there is reason to believe that they are of
extreme tenuity, "as rare as vacuum." The smallest
stars have been seen shining through their most
brilliant portions with undiminished lustre.

After the nucleus has been formed it begins to
throw out bright jets directed toward the sun. A
stream, and sometimes several streams, of light also
project sunward from the nucleus, occasionally ap-
pearing like a stunted tail directed oppositely to the
real tail. Symmetrical envelopes which, seen in
section, appear as half circles or parabolas, rise sun-
ward from the nucleus, forming a concentric series.
The ends of these stream backward into the tail, to
which they seem to supply material. Ordinarily the
formation of these ejections and envelopes is attended
by intense agitation of the nucleus, which twists and
turns, swinging and gyrating with an appearance
of the greatest violence. Sometimes the nucleus is
seen to break up into several parts. The entire heads
of some comets have been split asunder in passing
close around the sun; the comet of 1882 retreated into
space after its perihelion passage with five heads in-
stead of the one that it had originally, and each of
these heads had its own tail!

The possession of the spectroscope has enabled
astronomers during later years to study the chemical
composition of comets by analyzing their light. At

171

CURIOSITIES OF THE SKY

first the only substances thus discovered in them were
hydro-carbon compounds, due evidently to the
gaseous envelopes in which some combination of
hydrogen with carbon existed. Behind this gaseous
spectrum was found a faint continuous spectrum
ascribed to the nucleus, which apparently both re-
flects the sunlight and gives forth the light of a glow-
ing solid or liquid. Subsequently sodium and iron
lines were found in cometary spectra. The presence
of iron would seem to indicate that some of these
bodies may be much more massive than observations
on their attractive effects have indicated. In some
recent comets, such as Morehouse's, in 1908, several
lines have been found, the origin of which is unknown.
Without going back of the nineteenth century we
may find records of some of the most extraordinary
comets that man has ever looked upon. In 1811,
still spoken of as "the year of the comet," because of
the wonderful vintage ascribed to the skyey visitor, a
comet shaped like a gigantic sword amazed the whole
world, and, as it remained visible for seventeen months,
was regarded by superstitious persons as a symbol
of the fearful happenings of Napoleon's Russian
campaign. This comet, the extraordinary size of
whose head, greatly exceeding that of the sun itself,
has already been mentioned, was also remarkable for
exhibiting so great a brilliancy without approaching
even to the earth's distance from the sun. But there
was once a comet (and only once — in the year 1729)
which never got nearer to the sun than four times the
distance of the earth and yet appeared as a formid-
able object in the sky. As Professor Young has re-

172

STRANGE ADVENTURES OF COMETS

marked, "it must have been an enormous comet to
be visible from such a distance." And we are to
remember that there were no great telescopes in the
year 1729. That comet affects the imagination like
a phantom of space peering into the solar system, dis-
playing its enormous train afar off (which, if it had
approached as near as other comets, would probably
have become the celestial wonder of all human
memory), and then turning away and vanishing in the
depths of immensity.

In 1843 a comet appeared which was so brilliant
that it could be seen in broad day close beside the
sun! This was the first authenticated instance of
that kind, but the occurrence was to be repeated, as
we shall see in a moment, less than forty years later.

The splendid comet of 1858, usually called Donati's,
is remembered by many persons yet living. It was,
perhaps, both as seen by the naked eye and with the
telescope, the most beautiful comet of which we have
any record. It too marked a rich vintage year, still
remembered in the vineyards of France, where there
is a popular belief that a great comet ripens the grape
and imparts to the wine a flavor not attainable by
the mere skill of the cultivator. There are " comet
wines," carefully treasured in certain cellars, and
brought forth only when their owner wishes to treat
his guests to a sip from paradise.

The year 1861 saw another very remarkable comet,
of an aspect strangely vast and diffuse, which is
believed to have swept the earth with its immense
tail when it passed between us and the sun on the
night of June 3oth, an event which produced no other

CURIOSITIES OF THE SKY

known effect than the appearance of an unwonted
amount of scattered light in the sky.

The next very notable comet was the "Great
Southern Comet" of 1880, which was not seen from
the northern hemisphere. It mimicked the aspect
of the famous comet of 1843, and to the great sur-
prise of astronomers appeared to be travelling in the
same path. This proved to be the rising of the
curtain for an astronomical sensation unparalleled in
its kind; for two years later another brilliant comet
appeared, first in the southern hemisphere, and it too
followed the same track. The startling suggestion was
now made that this comet was identical with those
of 1843 and 1880, its return having been hastened by
the resistance experienced in passing twice through the
coronal envelope, and there were some who thought
that it would now swing swiftly round and then
plunge straight into the sun, with consequences that
might be disastrous to us on account of the "flash
of heat" that would be produced by the impact.
Nervous people were frightened, but observation soon
proved that the danger was imaginary, for although
the comet almost grazed the sun, and must have
rushed through two or three million miles of the
coronal region, no retardation of its immense velocity
was perceptible, and it finally passed away in a
damaged condition, as before remarked, and has never
since appeared.

Then the probable truth was perceived — viz., that
the three comets (1843, 1880, and 1882) were not
one identical body, but three separate ones all travel-
ling in the same orbit. It was found, too, that a

STRANGE ADVENTURES OF COMETS

comet seen in 1668 bore similar insignia of relation-
ship. The natural inference was that these four
bodies had once formed a single mass which had
been split apart by the disruptive action of the sun.
Strength was lent to this hypothesis by the fact that
the comet of 1882 was apparently torn asunder dur-
ing its perihelion passage, retreating into space in a
dissevered state. But Prof. George Forbes has a
theory that the splitting of the original comet ary mass
was effected by an unknown planet, probably greater
than Jupiter, situated at a hundred times the earth's
distance from the sun, and revolving in a period of a
thousand years. He supposes that the original comet
was not that of 1668, but one seen in 1556, which has
since been "missing," and that its disruption occurred
from an encounter with the supposititious planet
about the year 1700. Truly from every point of view
comets are the most extraordinary of adventurers!

The comet of 1882 was likewise remarkable for
being visible, like its predecessor of 1843, m fall day-
light in close proximity to the sun. The story of its
detection when almost in contact with the solar disk
is dramatic. It had been discovered in the southern
hemisphere only a couple of weeks before its perihelion,
which occurred on September i7th, and on the fore-
noon of that day it was seen by Doctor Common in
England, and by Doctor Elkin and Mr. Finlay at the
Cape of Good Hope, almost touching the sun. It
looked like a dazzling white bird with outspread
wings. The southern observers watched it go right
into the sun, when it instantly disappeared. What
had happened was that the comet in passing its

CURIOSITIES OF THE SKY

perihelion point had swung exactly between the earth
and the sun. On the following morning it was seen
from all parts of the world close by the sun on the
opposite side, and it remained thus visible for three
days, gradually receding from the solar disk. It then
became visible for northern observers in the morning
sky before sunrise, brandishing a portentous sword-
shaped tail which, if it had been in the evening sky,
would have excited the wonder of hundreds of millions,
but situated where it was, comparatively few ever saw it.
The application of photography to the study of
comets has revealed many curious details which
might otherwise have escaped detection, or at best
have remained subject to doubt. It has in particular
shown not only the precise form of the tails, but the
remarkable vicissitudes that they undergo. Professor
Barnard's photographs of Brooks' comet in 1893
suggested, by the extraordinary changes in the form
of the tail which they revealed, that the comet was
encountering a series of obstructions in space which
bent and twisted its tail into fantastic shapes. The
reader will observe the strange form into which the
tail was thrown on the night of October 2ist. A
cloud of meteors through which the comet was passing
might have produced such deformations of its tail.
In the photograph of Daniels' comet of 1907, a curious
striping of the tail will be noticed. The short bright
streaks seen in the photograph, it may be explained,
are the images of stars which are drawn out into lines
in consequence of the fact that the photographic
telescope was adjusted to follow the motion of the
comet while the stars remained at rest.

176

DANIELS COMET. AUGUST II, 1907

STRANGE ADVENTURES OF COMETS

But the adventures of comets are not confined to
possible encounters with unknown obstacles. We
have referred to the fact that the great planets, and
especially Jupiter, frequently interfere with the
motions of comets. This interference is not limited to
the original alteration of their orbits from possible
parabolas to ellipses, but is sometimes exercised again
and again, turning the bewildered comets into
elliptical paths of all degrees of eccentricity. A
famous example of this kind of planetary horse-play
is furnished by the story of LexelFs missing comet.
This comet was first seen in 1770. Investigation
showed that it was moving in an orbit which should
bring it back to perihelion every five and a half years ;
yet it had never been seen before and, although often
searched for, has never been seen since. Laplace and
Leverrier proved mathematically that in 1767 it
had approached so close to Jupiter as to be involved
among the orbits of his satellites. What its track
had been before is not known, but on that occasion the
giant planet seized the interloper, threw it into a short
elliptic orbit, and sent it, like an arrested vagrant, to
receive sentence at the bar of the sun. On this
journey it passed within less than 1,500,000 miles of
the earth. The form of orbit which Jupiter had im-
pressed required, as we have said, its return in about
five and a half years; but soon after 1770 it had the
misfortune a second time to encounter Jupiter at
close range, and he, as if dissatisfied with the leniency
of the sun, or indignant at the stranger's familiarity,
seized the comet and hurled it out of the system, or
at any rate so far away that it has never since been

179

CURIOSITIES OF THE SKY

able to rejoin the family circle that basks in trn
immediate rays of the solar hearth. Nor is this the
only instance in which Jupiter has dealt summarily
with small comets that have approached him with
too little deference.

The function which Jupiter so conspicuously ful-
fils as master of the hounds to the sun is worth con-
sidering a little more in detail. To change the figure,
imagine the sun in its voyage through space to be
like a majestic battleship surrounded by its scouts.
Small vessels (the comets), as they are overhauled
by the squadron, are taken in charge by the scouts,
with Jupiter for their chief, and are forced to accom-
pany the fleet; but not all are impressed. If a strange
comet undertakes to run across Jupiter's bows the
latter brings it to, and makes prize of it by throwing
it into a relatively small ellipse with the sun for its
focus. Thenceforth, unless, as happened to the un-
happy comet of Lexell, it encounters Jupiter again
in such a way as to be diverted by him into a more
distant orbit, it can never get away. About thirty
comets are now known to have thus been captured
by the great planet, and they are called "Jupiter's
Comet Family." But, on the other hand, if a wan-
dering comet crosses the wake of the chief planetary
scout the latter simply drives it away by accelerating
its motion and compels it to steer off into open space.
The transformation of comets into meteors will be
considered in the next chapter, but here, in passing,
mention may be made of the strange fate of one mem-
ber of Jupiter's family, Biela's comet, which, having
become overbold in its advances to its captor, was,

i So

STRANGE ADVENTURES OF COMETS

after a few revolutions in its impressed orbit, torn to
pieces and turned into a flock of meteors.

And now let us return to the mystery of comets'
tails. That we are fully justified in speaking of the
tails of comets as mysterious is proved by the dec-
laration of Sir John Herschel, who averred, in so
many words, that "there is some profound secret and
mystery of nature concerned in this phenomenon,"
and this profound secret and mystery has not yet been
altogether cleared up. Nevertheless, the all-explain-
ing hypothesis of Arrhenius offers us once more a
certain amount of aid. Comets' tails, Arrhenius
assures us, are but another result of the pressure of
light. The reader will recall the applications of this
theory to the Zodiacal Light and the Aurora. In the
form in which we now have to deal with it, the sup-
position is made that as a comet approaches the sun
eruptions of vapor, due to the solar heat, occur in its
nucleus. These are naturally most active on the
side which is directly exposed to the sun, whence the
appearance of the immense glowing envelopes that
surround the nucleus on the sunward side. Among the
particles of hydro-carbon, and perhaps solid carbon
in the state of fine dust, which are thus set free there
will be many whose size is within the critical limit
which enables the light-waves from the sun to drive
them away. Clouds of such particles, then, will
stream off behind the advancing comet, producing the
appearance of a tail. This accounts for the fact that
the tails of comets are always directed away from
the sun, and it also explains the varying forms of the
tails and the extraordinary changes that they undergo.

xo 183

CURIOSITIES OF THE SKY

The speed of the particles driven before the light-
waves must depend upon their size and weight, the
lightest of a given size travelling the most swiftly.
By accretion certain particles might grow, thus losing
velocity and producing the appearance of bunches
in the tail, such as have been observed. The hypoth-
esis also falls in with the researches of Bredichin,
who has divided the tails of comets into three principal
classes — viz.: (i) Those which appear as long, straight
rays; (2) Those which have the form of curved plumes
or scimitars; (3) Those which are short, brushy, and
curved sharply backward along the comet's path.
In the first type he calculates the repulsive force at
from twelve to fifteen times the force of gravity; in
the second at from two to four times; and in the
third at about one and a half times. The straight
tails he ascribes to hydrogen because the hydrogen
atom is the lightest known; the sword-shaped tails
to hydro-carbons; and the stumpy tails to vaporized
iron. It will be seen that, if the force driving off the
tails is that which Arrhenius assumes it to be, the
forms of those appendages would accord with those
that Bredichin 's theory calls for. At the same time
we have an explanation of the multiple tails with which
some comets have adorned themselves. The comet
of 1744, for instance, had at one time no less than
seven tails spread in a wide curved brush behind it.
Donati's comet of 1858 also had at least two tails,
the principal one sword-shaped and the other long,
narrow, and as straight as a rule. According to Bred-
ichin, the straight tail must have been composed of
hydrogen, and the other of some form of hydro-carbon

184

STRANGE ADVENTURES OF COMETS

whose atoms are heavier than those of hydrogen, and,
consequently, when swept away by the storm of light-
waves, followed a curvature depending upon the
resultant of the forces operating upon them. The
seven tails of the comet of 1744 presented a kind of
diagram graphically exhibiting its complex composi-
tion, and, if we knew a little more about the con-
stituents of a comet, we might be able to say from
the amount of curvature of the different tails just
what were the seven substances of which that comet
consisted.

If these theories seem to the reader fantastic, at
any rate they are no more fantastic than the phenom-
ena that they seek to explain.

XI

METEORS, FIRE-BALLS, AND METEORITES

ONE of the most terrorizing spectacles with which
the heavens have ever caused the hearts of men
to quake occurred on the night of November 13, 1833.
On that night North America, which faced the storm,
was under a continual rain of fire from about ten
o'clock in the evening until daybreak.

The fragments of a comet had struck the earth.

But the meaning of what had happened was not
discovered until long afterward. To the astronomers
who, with astonishment not less than that of other
people, watched the wonderful scene, it was an un-
paralleled "shower of meteors." They did not then
suspect that those meteors had once formed the head
of a comet. Light dawned when, a year later, Prof.
Denison Olmstead, of Yale College, demonstrated that
the meteors had all moved in parallel orbits around
the sun, and that these orbits intersected that of the
earth at the point where our planet happened to be
on the memorable night of November i3th. Professor
Olmstead even went so far as to suggest that the
cloud of meteors that had encountered the earth
might form a diffuse comet ; but full recognition of the
fact that they were cometary debris came later, as

186

METEORS, FIRE-BALLS, METEORITES

the result of further investigation. The key to the
secret was plainly displayed in the spectacle itself,
and was noticed without being understood by thou-
sands of the terror-stricken beholders. It was an
umbrella of fire that had opened overhead and covered
the heavens ; in other words, the meteors all radiated
from a particular point in the constellation Leo, and,
being countless as the snowflakes in a winter tempest,
they ribbed the sky with fiery streaks. Professor
Olmstead showed that the radiation of the meteors
from a fixed point was an effect of perspective, and
in itself a proof that they were moving in parallel
paths when they encountered the earth. The fact
was noted that there had been a similar, but in-
comparably less brilliant, display of meteors on the
same day of November, 1832, and it was rightly con-
cluded that these had belonged to the same stream,
although the true relationship of the phenomena was
not immediately apprehended. Olmstead ascribed
to the meteors a revolution about the sun once in
every six months, bringing them to the intersection
of their orbit with that of the earth every November
1 3th; but later investigators found that the real
period was about thirty-three and one-quarter years,
so that the great displays were due three times in a
century, and their return was confidently predicted
for the year 1866. The appearance of the meteors
in 1832, a year before the great display, was ascribed
to the great length of the stream which they formed
in space — so great that they required more than two
years to cross the earth's orbit. In 1832 the earth had
encountered a relatively rare part of the stream,

187

CURIOSITIES OF THE SKY

but in 1833, on returning to the crossing-place, it
found there the richest part of the stream pouring
across its orbit. This explanation also proved to be
correct, and the predicted return in 1866 was duly
witnessed, although the display was much less brilliant
than in 1833. It was followed by another in 1867.

In the mean time Olmstead's idea of a cometary
relationship of the meteors was demonstrated to be
correct by the researches of Schiaparelli and others,
who showed that not only the November meteors, but
those of August, which are seen more or less abun-
dantly every year, travelled in the tracks of well-
known comets, and had undoubtedly an identical
origin with those comets. In other words the comets
and the meteor-swarms were both remnants of original
masses which had probably been split up by the action
of the sun, or of some planet to which they had made
close approaches. The annual periodicity of the
August meteors was ascribed to the fact that the
separation had taken place so long ago that the
meteors had become distributed all around the orbit,
in consequence of which the earth encountered
some of them every year when it arrived at the
crossing - point. Then Leverrier showed that the
original comet associated with the November meteors
was probably brought into the system by the influence
of the planet Uranus in the year 126 of the Christian
era. Afterward Alexander Herschel identified the
tracks of no less than seventy-six meteor - swarms
(most of them inconspicuous) with those of comets.
The still more recent researches of Mr. W. F. Denning
make it probable that there are no meteors which

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METEORS, FIRE-BALLS, METEORITES

do not belong to a flock or system probably formed
by the disintegration of a cometary mass; even the
apparently sporadic ones which shoot across the sky,
"lost souls in the night," being members of flocks
which have become so widely scattered that the earth
sometimes takes weeks to pass through the region of
space where their paths lie.

The November meteors should have exhibited an-
other pair of spectacles in 1899 and 1900, and their
failure to do so caused at first much disappointment,
until it was made plain that a good reason existed
for their absence. It was found that after their last
appearance, in 1867, they had been disturbed in their
movements by the planets Jupiter and Saturn, whose
attractions had so shifted the position of their orbit
that it no longer intersected that of the earth, as it
did before. Whether another planetary interference
will some time bring the principal mass of the Novem-
ber meteors back to the former point of intersection
with the earth's orbit is a question for the future to
decide. It would seem that there may be several
parallel streams of the November meteors, and that
some of them, like those of August, are distributed
entirely around the orbit, so that every mid-November
we see a few of them.

We come now to a very remarkable example of the
disintegration of a comet and the formation of a
meteor - stream. In 1826 Biela, of Josephstadt,
Austria, discovered a comet to which his name was
given. Calculation showed that it had an orbital
period of about six and a half years, belonging to
Jupiter's "family." On one of its returns, in 1846,

191

CURIOSITIES OF THE SKY

it astonished its watchers by suddenly splitting in two.
The two comets thus formed out of one separated to
a distance of about one hundred and sixty thousand
miles, and then raced side by side, sometimes with a
curious ligature connecting them, like Siamese twins,
until they disappeared together in interplanetary
space. In 1852 they came back, still nearly side by
side; but now the distance between them had in-
creased to a million and a quarter of miles. After
that, at every recurrence of their period, astronomers
looked for them in vain, until 1872, when an amazing
thing happened. On the night of November 28th,
when the earth was crossing the plane of the orbit of
the missing comet, a brilliant shower of meteors
burst from the northern sky, travelling nearly in the
track which the comet should have pursued. The
astronomers were electrified. Klinkerfues, of Gottin-
gen, telegraphed to Pogson, of Madras: "Biela touched
earth; search near Theta Centauri" Pogson searched
in the place indicated and saw a cometary mass re-
treating into the southern heavens, where it was soon
swallowed from sight!

Since then the Biela meteors have been among the
recognized periodic spectacles of the sky, and few if
any doubt that they represent a portion of the missing
comet whose disintegration began with the separation
into two parts in 1846. The comet itself has never
since been seen. The first display of these meteors,
sometimes called the "Andromedes," because they
radiate from the constellation Andromeda, was re-
markable for the great brilliancy of many of the fire-
balls that shot among the shower of smaller sparks,

192

SECTION OF THE ATMOSPHERE UP TO
100 KILOMETERS

Showing the mean elevation at
which meteorites and meteors make
their appearance. Below are shown
the elevation of Mount Everest; the
.highest manned balloon ascent by
M. Berson; the height of cirrus clouds;
the highest free balloon ascent; and
the elevation attained by the clouds
^of fire-dust ejected by the Krakatoa
eruption in 1883. (From La Nature.)

METEORS, FIRE-BALLS, METEORITES

some of which were described as equalling the full
moon in size. None of them is known to have reached
the earth, but during the display of the same meteors
in 1885 a meteoric mass fell at Mazapil in Northern
Mexico (it is now in the Museum at Vienna), which
many have thought may actually be a piece of the
original comet of Biela. This brings us to the second
branch of our subject.

More rare than meteors or falling stars, and more
startling, except that they never appear in showers,
are the huge balls of fire which occasionally dart
through the sky, lighting up the landscapes beneath
with their glare, leaving trains of sparks behind them,
often producing peals of thunder when they explode,
and in many cases falling upon the earth and burying
themselves from a few inches to several feet in the
soil, from which, more than once, they have been
picked up while yet hot and fuming. These balls
are sometimes called bolides. They are not really
round in shape, although they often look so while
traversing the sky, but their forms are fragmentary,
and occasionally fantastic. It has been supposed
that their origin is different from that of the true
meteors ; it has even been conjectured that they may
have originated from the giant volcanoes of the moon
or have been shot out from the sun during some of the
tremendous explosions that accompany the formation
of eruptive prominences. By the same reasoning
some of them might be supposed to have come from
some distant star. Others have conjectured that they
are wanderers in space, of unknown origin, which the
earth encounters as it journeys on, and Lord Kelvin

CURIOSITIES OF THE SKY

made a suggestion which has become classic because
of its imaginative reach — viz., that the first germs of
life may have been brought to the earth by one of
these bodies, "a fragment of an exploded world."

It is a singular fact that astronomers and scien-
tific men in general were among the last to admit
the possibility of solid masses falling from the sky.
The people had believed in the reality of such phenom-
ena from the earliest times, but the savants shook
their heads and talked of superstition. This was the
less surprising because no scientifically authenticated
instance of such an occurrence was known, and the
stones popularly believed to have fallen from the sky
had become the objects of worship or superstitious
reverence, a fact not calculated to recommend them
to scientific credence. The celebrated "black stone"
suspended in the Kaaba at Mecca is one of these
reputed gifts from heaven; the "Palladium " of ancient
Troy was another; and a stone which fell near En-
sisheim, in Germany, was placed in a church as an
object to be religiously venerated. Many legends of
falling stones existed in antiquity, some of them curi-
ously transfigured by the imagination, like the "Lion
of the Peloponnesus," which was said to have sprung
down from the sky upon the Isthmus of Corinth. But
near the beginning of the nineteenth century, in 1803,
a veritable shower of falling stones occurred at L'Aigle,
in Northern France, and this time astronomers took
note of the phenomenon and scientifically investigated
it. Thousands of the strange projectiles came from
the sky on this occasion, and were scattered over a
wide area of country, and some buildings were hit.

196

METEORS, FIRE-BALLS, METEORITES

Four years later another shower of stones occurred at
Weston, Conn., numbering thousands of individuals.
The local alarm created in both cases was great, as
well it might be, for what could be more intimidating
than to find the blue vault of heaven suddenly hurling
solid missiles at the homes of men? After these
occurrences it was impossible for the most skeptical
to doubt any longer, and the regular study of "aero-
lites," or "meteorites," began.

One of the first things recognized was the fact that
fire-balls are solid meteorites in flight, and not gaseous
exhalations in the air, as some had assumed. They
burn in the air during their flight, and sometimes, per-
haps, are entirely consumed before reaching the
ground. Their velocity before entering the earth's
atmosphere is equal to that of the planets in their
orbits — viz., from twenty to thirty miles per second —
a fact which proves that the sun is the seat of the
central force governing them. Their burning in the
air is not difficult to explain; it is the heat of friction
which so quickly brings them to incandescence. Cal-
culation shows that a body moving through the air
at a velocity of about a mile per second will be brought,
superficially, to the temperature of "red heat" by
friction with the atmosphere. If its velocity is twenty
miles per second the temperature will become thou-
sands of degrees. This is the state of affairs with a
meteorite rushing into the earth's atmosphere; its
surface is liquefied within a few seconds after the
friction begins to act, and the melted and vaporized
portion of its mass is swept backward, forming the
train of sparks that follows every great fire-ball, How-

197

CURIOSITIES OF THE SKY

ever, there is one phenomenon connected with the
trains of meteorites which has never been satisfac-
torily explained: they often persist for long periods
of time, drifting and turning with the wind, but not
ceasing to glow with a phosphorescent luminosity.
The question is, Whence comes this light? It must
be light without heat, since the fine dust or vapor
of which the train can only consist would not retain
sufficient heat to render it luminous for so long a time.
An extremely remarkable incident of this kind oc-
curred on February 22, 1909, when an immense fire-
ball that passed over southern England left a train
that remained visible during two hours, assuming
many curious shapes as it was drifted about by cur-
rents in the air.

But notwithstanding the enormous velocity with
which meteorites enter the air they are soon slowed
down to comparatively moderate speed, so that when
they disappear they are usually travelling not faster
than a mile a second. The courses of many have been
traced by observers situated along their track at
various points, and thus a knowledge has been ob-
tained of their height above the ground during their
flight and of the length of their visible courses. They
generally appear at an elevation of eighty or a hun-
dred miles, and are seldom visible after having de-
scended to within five miles of the ground, unless the
observer happens to be near the striking-point, when
he may actually witness the fall. Frequently they
burst while high in the air and their fragments are
scattered like shrapnel over the surface of the ground,
sometimes covering an area of several square miles,

198

A METEOR PHOTOGRAPHED IN FLIGHT

METEORS, FIRE-BALLS, METEORITES

but of course not thickly; different fragments of the
same meteorite may reach the ground at points several
miles apart. The observed length of their courses in
the atmosphere varies from fifty to five hundred
miles. If they continued a long time in flight after
entering the air, even the largest of them would prob-
ably be consumed to the last scrap, but their fiery
career is so short on account of their great speed that
the heat does not have time to penetrate very deeply,
and some that have been picked up immediately after
their fall have been found cold as ice within. Their
size after reaching the ground is variable within wide
limits ; some are known which weigh several tons, but
the great majority weigh only a few pounds and many
only a few ounces.

Meteorites are of two kinds: stony meteorites and
iron meteorites. The former outnumber the latter
twenty to one; but many stone meteorites contain
grains of iron. Nickel is commonly found in iron
meteorites, so that it might be said that that redoubt-
able alloy nickel-steel is of cosmical invention. Some
twenty-five chemical elements have been found in
meteorites, including carbon and the "sun-metal,"
helium. The presence of the latter is certainly high-
ly suggestive in connection with the question of the
origin of meteorites. The iron meteorites, besides
metallic iron and nickel, of which they are almost en-
tirely composed, contain hydrogen, helium, and car-
bonic oxide, and about the only imaginable way in
which these gases could have become absorbed in the
iron would be through the immersion of the latter
while in a molten or vaporized state in a hot and

201

CURIOSITIES OF THE SKY

dense atmosphere composed of them, a condition
which we know to exist only in the envelopes of the
sun and the stars.

The existence of carbon in the Canyon Diablo iron
meteorites is attended by a circumstance of the most
singular character — a very "fairy tale of science."
In some cases the carbon has become diamond! These
meteoric diamonds are very small; nevertheless, they
are true diamonds, resembling in many ways the little
black gems produced by Moissan's method with the
aid of the electric furnace. The fact that they are
found embedded in these iron meteorites is another
argument in favor of the hypothesis of the solar or
stellar origin of the latter. To appreciate this it is
necessary to recall the way in which Moissan made his
diamonds. It was by a combination of the effects of
great heat, great pressure, and sudden or rapid super-
ficial cooling on a mass of iron containing carbon.
When he finally broke open his iron he found it a
pudding stuffed with miniature black diamonds.
When a fragment of the Canyon Diablo meteoric iron
was polished in Philadelphia over fifteen years ago it
cut the emery-wheel to pieces, and examination
showed that the damage had been effected by micro-
scopic diamonds peppered through the mass. How
were those diamonds formed? If the sun or Sirius
was the laboratory that prepared them, we can get a
glimpse at the process of their formation. There is
plenty of heat, plenty of pressure, and an abundance
of vaporized iron in the sun and the stars. When a
great solar eruption takes place, masses of iron which
have absorbed carbon may be shot out with a velocity

202

METEORS, FIRE-BALLS, METEORITES

whidi forbids their return. Plunged into the fright-
ful cold of space, their surfaces are quickly cooled, as
Moissan cooled his prepared iron by throwing it into
water, and thus the requisite stress is set up within,
and, as the iron solidifies, the included carbon crys-
tallizes into diamonds. Whether this explanation has
a germ of truth in it or not, at any rate it is evident
that iron meteorites were not created in the form in
which they come to us; they must once have been
parts of immeasurably more massive bodies than
themselves.

The fall of meteorites offers an appreciable, though
numerically insignificant, peril to the inhabitants of
the earth. Historical records show perhaps three or
four instances of people being killed by these bodies.
But for the protection afforded by the atmosphere,
which acts as a very effective shield, the danger
would doubtless be very much greater. In the
absence of an atmosphere not only would more
meteorites reach the ground, but their striking force
would be incomparably greater, since, as we have
seen, the larger part of their original velocity is de-
stroyed by the resistance of the air. A meteorite
weighing many tons and striking the earth with a
velocity of twenty or thirty miles per second, would
probably cause frightful havoc.

It is a singular fact that recent investigations
seem to have proved that an event of this kind actu-
ally happened in North America — perhaps not longer
than a thousand or two thousand years ago. The
scene of the supposed catastrophe is in northern
central Arizona, at Coon Butte, where there is a

203

CURIOSITIES OF THE SKY

nearly circular crater in the middle of a circular
elevation or small mountain. The crater is some-
what over four thousand feet in diameter, and the
surrounding rim, formed of upturned strata and
ejected rock fragments, rises at its highest point
one hundred and sixty feet above the plain. The
crater is about six hundred feet in depth — that is, from
the rim to the visible floor or bottom of the crater.
There is no evidence that volcanic action has ever
taken place in the immediate neighborhood of Coon
Butte. The rock in which the crater has been made
is composed of horizontal sandstone and limestone
strata. Between three hundred and four hundred
million tons of rock fragments have been detached,
and a large portion hurled by some cause out of the
crater. These fragments lie concentrically distribut-
ed around the crater, and in large measure form the
elevation known as Coon Butte. The region has been
famous for nearly twenty years on account of the
masses of meteoric iron found scattered about and
known as the "Canyon Diablo" meteorites. It was
one of these masses, which consist of nickel-iron con-
taining a small quantity of platinum, and of which
in all some ten tons have been recovered for sale to
the various collectors throughout the world, that as
before mentioned destroyed the grinding - tool at
Philadelphia through the cutting power of its em-
bedded diamonds. These meteoric irons are scattered
about the crater-hill, in concentric distribution, to a
maximum distance of about five miles. When the
suggestion was first made in 1896 that a monster
meteorite might have created by its fall this singular

204

METEORS, FIRE-BALLS, METEORITES

lone crater in stratified rocks, it was greeted with in-
credulous smiles; but since then the matter has as-
sumed a different aspect. The Standard Iron Com-
pany, formed by Messrs. D. M. Barringer, B. C.
Tilghman, E. J. Bennitt, and S. J. Holsinger, having
become, in 1903, the owner of this freak of nature,
sunk shafts and bored holes to a great depth in the
interior of the crater, and also trenched the slopes of
the mountain, and the result of their investigations
has proved that the meteoric hypothesis of origin is
correct. (See the papers published in the Proceedings
of the Academy of Natural Sciences of Philadelphia,
December, 1905, wherein it is proved that the United
States Geological Survey was wrong in believing this
crater to have been due to a steam explosion. Since
that date there has been discovered a great amount
of additional confirmatory proof.) Material of unmis-
takably meteoric origin was found by means of the
drills, mixed with crushed rock, to a depth of six
hundred to seven hundred feet below the floor of the
crater, and a great deal of it has been found admixed
with the ejected rock fragments on the outer slopes
of the mountain, absolutely proving synchronism be-
tween the two events, the formation of this great
crater and the falling of the meteoric iron out of the
sky. The drill located in the bottom of the crater
was sent, in a number of cases, much deeper (over one
thousand feet) into unaltered horizontal red sand-
stone strata, but no meteoric material was found
below this depth (seven hundred feet, or between
eleven and twelve hundred feet below the level of the
surrounding plain), which has been assumed as being
« 207

CURIOSITIES OF THE SKY

about the limit of penetration. It is not possible
to sink a shaft at present, owing to the water which
has drained into the crater, and which forms, with
the finely pulverized sandstone, a very troublesome
quicksand encountered at about two hundred feet
below the visible floor of the crater. As soon as this
water is removed by pumping it will be easy to explore
the depths of the crater by means of shafts and drifts.
The rock strata (sandstone and limestone) of which
the walls consist present every appearance of having
been violently upturned by a huge body penetrating
the earth like a cannon-ball. The general aspect of
the crater strikingly resembles the impression made
by a steel projectile shot into an armor-plate. Mr.
Tilghman has estimated that a meteorite about five
hundred feet in diameter and moving with a velocity
of about five miles per second would have made just
such a perforation upon striking rocks of the character
of those found at this place. There was some fusion
of the colliding masses, and the heat produced some
steam from the small amount of water in the rocks.
As a result there has been found at depth a consider-
able amount of fused quartz (original sandstone) , and
with it innumerable particles or sparks of fused
nickel-iron (original meteorite). A projectile of that
size penetrating eleven to twelve hundred feet into
the rocky shell of the globe must have produced a
shock which was perceptible several hundred miles
away.

The great velocity ascribed to the supposed mete-
orite at the moment of striking could be accounted
for by the fact that it probably plunged nearly

208

METEORS, FIRE-BALLS, METEORITES

vertically downward, for it formed a circular crater
in the rocky crust of the earth. In that case it
would have been less retarded by the resistance
of the atmosphere than are meteorites which enter the
air at a lower angle and shoot ahead hundreds of
miles until friction has nearly destroyed their original
motion when they drop upon the earth. Some
meteoric masses of great size, such as Peary's iron
meteorite found at Cape York, Greenland, and the
almost equally large mass discovered at Bacubirito,
Mexico, appear to have penetrated but slightly on
striking the earth. This may be explained by sup-
posing that they pursued a long, horizontal course
through the air before falling. The result would be
that, their original velocity having been practically de-
stroyed, they would drop to the ground with a velocity
nearly corresponding to that which gravity would
impart within the perpendicular distance of their
final fall. A six-hundred-and-sixty-pound meteorite,
which fell at Knyahinya, Hungary, striking at an
angel of 27° from the vertical, penetrated the ground
to a depth of eleven feet.

It has been remarked that the Coon Butte meteor-
ite may have fallen not longer ago than a few thou-
sand years. This is based upon the fact that the
geological indications favor the supposition that the
event did not occur more than five thousand years
ago, while on the other hand the rings of growth
in the cedar-trees growing on the slopes of the crater
show that they have existed there about seven hun-
dred years. Prof. William H. Pickering has recently
correlated this with an ancient chronicle which states

211

CURIOSITIES OF THE SKY

that at Cairo, Egypt, in the year 1029, "many stars
passed with a great noise." He remarks that Cairo
is about 100°, by great circle, from Coon Butte, so
that if the meteorite that made the crater was a
member of a flock of similar bodies which encountered
the earth moving in parallel lines, some of them might
have traversed the sky tangent to the earth's surface
at Cairo. That the spectacle spoken of in the chron-
icle was caused by meteorites he deems exceedingly
probable because of what is said about ' ' a great noise ' ' ;
meteorites are the only celestial phenomena attended
with perceptible sounds. Professor Pickering con-
jectures that this supposed flock of great meteorites
may have formed the nucleus of a comet which struck
the earth, and he finds confirmation of the idea in the
fact that out of the ten largest meteorites known, no
less than seven were found within nine hundred miles
of Coon Butte. It would be interesting if we could
trace back the history of that comet, and find out wrhat
malicious planet caught it up in its innocent wan-
derings and hurled it with so true an aim at the earth!
This remarkable crater is one of the most interesting
places in the world, for there is absolutely no record
of such a mass, possibly an iron-headed comet, from
outer space having come into collision with our earth.
The results of the future exploration of the depths of
the crater will be awaited with much interest.

XII

THE WRECKING OP THE MOON

HPHERE are sympathetic moods under whose in-
1 fluence one gazes with a certain poignant ten-
derness at the worn face of the moon; that little
''fossil world" (the child of our mother earth, too)
bears such terrible scars of its brief convulsive life
that a sense of pity is awakened by the sight. The
moon is the wonder-land of the telescope. Those
towering mountains, whose "proud aspiring peaks"
cast silhouettes of shadow that seem drawn with india-
ink ; those vast plains, enchained with gentle winding
hills and bordered with giant ranges; those oval
"oceans," where one looks expectant for the flash of
wind-whipped waves; those enchanting "bays" and
recesses at the seaward feet of the Alps; those broad
straits passing between guardian heights incom-
parably mightier than Gibraltar; those locket-like
valleys as secluded among their mountains as the
Vale of Cashmere; those colossal craters that make
us smile at the pretensions of Vesuvius, Etna, and
Cotopaxi; those strange white ways which pass with
the unconcern of Roman roads across mountain, gorge,
and valley — all these give the beholder an irresistible
impression that it is truly a world into which he is

213

CURIOSITIES OF THE SKY

looking, a world akin to ours, and yet no more like
our world than Pompeii is like Naples. Its air, its
waters, its clouds, its life are gone, and only a skeleton
remains — a mute but eloquent witness to a cosmical
tragedy without parallel in the range of human
knowledge.

One cannot but regret that the moon, if it ever was
the seat of intelligent life, has not remained so until
our time. Think what the consequences would have
been if this other world at our very door had been
found to be both habitable and inhabited! We talk
rather airily of communicating with Mars by signals;
but Mars never approaches nearer than 35,000,000
miles, while the moon when nearest is only a little more
than 2 20 ,000 miles away. Given an effective magnify-
ing power of five thousand diameters, which will per-
haps be possible at the mountain observatories as
telescopes improve, and we should be able to bring
the moon within an apparent distance of about forty
miles, while the corresponding distance for Mars would
be more than seven thousand miles. But even with
existing telescopic powers we can see details on the
moon no larger than some artificial constructions on
the earth. St. Peter's at Rome, with the Vatican
palace and the great piazza, if existing on the moon,
would unquestionably be recognizable as something
else than a freak of nature. Large cities, with their
radiating lines of communication, would at once be-
tray their real character. Cultivated tracts, and the
changes produced by the interference of intelligent
beings, would be clearly recognizable. The electric
illumination of a large town at night would probably

214

THE WRECKING OF THE MOON

be markedly visible. Gleams of reflected sunlight
would come to us from the surfaces of the lakes and
oceans, and a huge "liner" traversing a lunar sea
could probably be followed by its trail of smoke. As
to communications by "wireless" signals, which cer-
tain enthusiasts have thought of in connection with
Mars, in the case of the moon they should be a rela-
tively simple matter, and the feat might actually be
accomplished. Think what a literature would grow
up about the moon if it were a living world ! Its very
differences from the earth would only accentuate its
interest for us. Night and day on the moon are each
two weeks in length; how interesting it would be to
watch the manner in which the lunarians dealt with
such a situation as that. Lunar and terrestrial history
would keep step with each other, and we should record
them both. Truly one might well wish to have a
neighbor world to study; one would feel so much the
less alone in space.

It is not impossible that the moon did at one time
have inhabitants of some kind. But, if so, they van-
ished with the disappearance of its atmosphere and
seas, or with the advent of its cataclysmic age. At the
best, its career as a living world must have been brief.
If the water and air were gradually absorbed, as some
have conjectured, by its cooling interior rocks, its sur-
face might, nevertheless, have retained them for long
ages; but if, as others think, their disappearance was
due to the escape of their gaseous molecules in con-
sequence of the inability of the relatively, small lunar
gravitation to retain them, then the final catastrophe
must have been as swift as it was inevitable. Ac-

215

CURIOSITIES OF THE SKY

cepting Darwin's hypothesis, that the moon was
separated from the earth by tidal action while both
were yet plastic or nebulous, we may reasonably con-
clude that it began its career with a good supply of
both water and air, but did not possess sufficient
mass to hold them permanently. Yet it may have
retained them long enough for life to develop in
many forms upon its surface; in fact, there are so
many indications that air and water have not always
been lacking to the lunar world that we are driven
to invent theories to explain both their former presence
and their present absence.

But whatever the former condition of the moon
may have been, its existing appearance gives it a
resistless fascination, and it bears so clearly the story
of a vast catastrophe sculptured on its rocky face that
the thoughtful observer cannot look upon it without
a feeling of awe. The gigantic character of the lunar
features impresses the beholder not less than the uni-
versality of the play of destructive forces which they
attest. Let us make a few comparisons. Take the
lunar crater called "Tycho," which is a typical ex-
ample of its kind. In the telescope Tycho appears as a
perfect ring surrounding a circular depression, in the
centre of which rises a group of mountains. Its
superficial resemblance to some terrestrial volcanic
craters is very striking. Vesuvius, seen from a point
vertically above, would no doubt look something like
that (the resemblance would have been greater when
the Monte del Cavallo formed a more complete circuit
about the crater cone) . But compare the dimensions.
The remains of the outer crater ring of Vesuvius are

216

THE CRATERS CLAVIUS, LONGOMONTANUS, TYCHO, ETC.

.

THE WRECKING OF THE MOON

perhaps half a mile in diameter, while the active crater
itself is only two or three hundred feet across at the
most; Tycho has a diameter of fifty- four miles! The
group of relatively insignificant peaks in the centre of
the crater floor of Tycho is far more massive than the
entire mountain that we call Vesuvius. The largest
known volcanic crater on the earth, Aso San, in Japan,
has a diameter of seven miles; it would take sixty
craters like Aso San to equal Tycho in area! And
Tycho, though one of the most perfect, is by no means
the largest crater on the moon. Another, called
"Theophilus," has a diameter of sixty- four miles, and
is eighteen thousand feet deep. There are hundreds
from ten to forty miles in diameter, and thousands
from one to ten miles. They are so numerous in
many places that they break into one another, like the
cells of a crushed honeycomb.

The lunar craters differ from those of the earth more
fundamentally than in the matter of mere size ; they
are not situated on the tops of mountains. If they were,
and if all the proportions were the same, a crater like
Tycho might crown a conical peak fifty or one hundred
miles high! Instead of being cavities in the summits
of mountains, the lunar craters are rather gigantic sink-
holes whose bottoms in many cases lie two or three
miles below the general surface of the lunar world.
Around their rims the rocks are piled up to a height
of from a few hundred to two or three thousand feet,
with a comparatively gentle inclination, but on the
inner side they fall away in gigantic broken precipices
which make the dizzy cliffs of the Matterhorn seem
but "lover's leaps." Down they drop, ridge below

219

CURIOSITIES OF THE SKY

ridge crag under crag, tottering wall beneath wall, un-
til, in a crater named " Newton," near the south lunar
pole, they attain a depth where the rays of the sun
never reach. Nothing more frightful than the spec-
tacle which many of these terrible chasms present can
be pictured by the imagination. As the lazy lunar
day slowly advances, the sunshine, unmitigated by
clouds or atmospheric veil of any kind, creeps across
their rims and begins to descend the opposite walls.
Presently it strikes the ragged crest of a ridge which
had lain hidden in such darkness as we never know
on the earth, and runs along it like a line of kindling
fire. Rocky pinnacles and needles shoot up into the
sunlight out of the black depths. Down sinks the
line of light, mile after mile, and continually new
precipices and cliffs are brought into view, until at
last the vast floor is attained and begins to be illumi-
nated. In the mean while the sun's rays, darting
across the gulf, have touched the summits of the
central peaks, twenty or thirty miles from the crater's
inmost edge, and they immediately kindle and blaze
like huge stars amid the darkness. So profound are
some of these awful craters that days pass before the
sun has risen high enough above them to chase the
last shadows from their depths.

Although several long ranges of mountains resem-
bling those of the earth exist on the moon, the great
majority of its elevations assume the crateriform as-
pect. Sometimes, instead of a crater, we find an
immense mountain ring whose form and aspect hard-
ly suggest volcanic action. But everywhere the true
craters are in evidence, even on the sea-beds, al-

220

THE WRECKING OF THE MOON

though they attain their greatest number and size
on those parts of the moon — covering sixty per cent,
of its visible surface — which are distinctly mountain-
ous in character and which constitute its most brill-
iant portions. Broadly speaking, the southwestern
half of the moon is the most mountainous and broken,
and the northeastern half the least so. Right down
through the centre, from pole to pole, runs a wonder-
ful line of craters and crateriform valleys of a magni-
tude stupendous even for the moon. Another similar
line follows the western edge. Three or four "seas"
are thrust between these mountainous belts. By the
effects of "libration" parts of the opposite hemi-
sphere of the moon which is turned away from the
earth are from time to time brought into view, and
their aspect indicates that that hemisphere resembles
in its surface features the one which faces the earth.
There are many things about the craters which seem
to give some warrant for the hypothesis which has
been particularly urged by Mr. W. K. Gilbert, that
they were formed by the impact of meteors; but
there are also many things which militate against
that idea, and, upon the whole, the volcanic theory
of their origin is to be preferred.

The enormous size of the lunar volcanoes is not so
difficult to account for when we remember how slight
is the force of lunar gravity as compared with that of
the earth. With equal size and density, bodies on
the moon weigh only one-sixth as much as on the
earth. Impelled by the same force, a projectile that
would go ten miles on the earth would go sixty miles
on the moon. A lunar giant thirty-five feet tall

221

CURIOSITIES OF THE SKY

would weigh no more than an ordinary son of Adam
weighs on his greater planet. To shoot a body from
the earth so that it would not drop back again, we
should have to start it with a velocity of seven miles
per second; a mile and a half per second would serve
on the moon. It is by no means difficult to believe,
then, that a lunar volcano might form a crater ring
eight or ten times broader than the greatest to be
found on the earth, especially when we reflect that
in addition to the relatively slight force of gravity,
the materials of the lunar crust are probably lighter
than those of our terrestrial rocks.

For similar reasons it seems not impossible that
the theory mentioned in a former chapter — that
some of the meteorites that have fallen upon the
earth originated from the lunar volcanoes — is well
founded. This would apply especially to the stony
meteorites, for it is hardly to be supposed that the
moon, at least in its superficial parts, contains much
iron. It is surely a scene most strange that is thus
presented to the mind's eye — that little attendant
of the earth's (the moon has only one-fiftieth of the
volume, and only one-eightieth of the mass of the
earth) firing great stones back at its parent planet!
And what can have been the cause of this furious
outbreak of volcanic forces on the moon? Evidently
it was but a passing stage in its history; it had en-
joyed more quiet times before. As it cooled down
from the plastic state in which it parted from the
earth, it became incrusted after the normal manner
of a planet, and then oceans were formed, its atmos-
phere being sufficiently dense to prevent the water

222

WESTERN PART OF THE MARE SERENITATIS

THE WRECKING OF THE MOON

from evaporating and the would-be oceans from dis-
appearing continually in mist. This, if any, must
have been the period of life in the lunar world. As
we look upon the vestiges of that ancient world buried
in the wreck that now covers so much of its surface,
it is difficult to restrain the imagination from pictur-
ing the scenes which were once presented there ; and,
in such a case, should the imagination be fettered?
We give it free rein in terrestrial life, and it rewards
us with some of our greatest intellectual pleasures.
The wonderful landscapes of the moon offer it an
ideal field with just enough half-hidden suggestions
of facts to stimulate its powers.

The great plains of the Mare Imbrium and the Mare
Serenitatis (the "Sea of Showers" and the "Sea of
Serenity"), bordered in part by lofty mountain
ranges precisely like terrestrial mountains, scalloped
along their shores with beautiful bays curving back
into the adjoining highlands, and united by a great
strait passing between the nearly abutting ends of
the "Lunar Apennines" and the "Lunar Caucasus,"
offer the elements of a scene of world beauty such as
it would be difficult to match upon our planet. Look
at the finely modulated bottom of the ancient sea in
Mr. Ritchey's exquisite photograph of the western
part of the Mare Serenitatis, where one seems to see
the play of the watery currents heaping the ocean
sands in waving lines, making shallows, bars, and
deeps for the mariner to avoid or seek, and affording
a playground for the creatures of the main. What
geologist would not wish to try his hammer on those
rocks with their stony pages of fossilized history?

225

CURIOSITIES OF THE SKY

There is in us an instinct which forbids us to think
that there was never any life there. If we could
visit the moon, there is not among us a person so
prosaic and unimaginative that he would not, the
very first thing, begin to search for traces of its in-
habitants. We would look for them in the deposits
on the sea bottoms; we would examine the shores
wherever the configuration seemed favorable for har-
bors and the sites of maritime cities — forgetting that
it may be a little ridiculous to ascribe to the ancient
lunarians the same ideas that have governed the de-
velopment of our race; we would search through the
valleys and along the seeming courses of vanished
streams; we would explore the mountains, not the
terrible craters, but the pinnacled chains that recall
our own Alps and Rockies ; seeking everywhere some
vestige of the transforming presence of intelligent
life. Perhaps we should find such traces, and per-
haps, with all our searching, we should find nothing
to suggest that life had ever existed amid that uni-
versal ruin.

Look again at the border of the "Sea of Serenity"
— what a name for such a scene! — and observe how
it has been rent with almost inconceivable violence,
the wall of the colossal crater Posidonius dropping
vertically upon the ancient shore and obliterating it,
while its giant neighbor, Le Monnier, opens a yawn-
ing mouth as if to swallow the sea itself. A scene
like this makes one question whether, after all, those
may not be right who have imagined that the so-called
sea bottoms are really vast plains of frozen lava
which gushed up in floods so extensive that even

226

MARE TRANQUILITATIS AND SURROUNDINGS

THE WRECKING OF THE MOON

the mighty volcanoes were half drowned in the fiery
sea. This suggestion becomes even stronger when
we turn to another of the photographs of Mr. Ritchey 's
wonderful series, showing a part of the Mare Tran-
quilitatis ("Sea of Tranquility " !) . Notice how near
the centre of the picture the outline of a huge ring
with radiating ridges shows through the sea bottom;
a fossil volcano submerged in a petrified ocean!
This is by no means the only instance in which a
buried world shows itself under the great lunar plains.
Yet, as the newer craters in the sea itself prove, the
volcanic activity survived this other catastrophe, or
broke out again subsequently, bringing more ruin to
pile upon ruin.

Yet notwithstanding the evidence which we have
just been considering in support of the hypothesis
that the "seas" are lava floods, Messrs. Loewy and
Puiseux, the selenographers of the Paris Observatory,
are convinced that these great plains bear character-
istic marks of the former presence of immense bodies
of water. In that case we should be forced to con-
clude that the later oceans of the moon lay upon vast
sheets of solidified lava ; and thus the catastrophe of
the lunar world assumes a double aspect, the earliest
oceans being swallowed up in molten floods issuing
from the interior, while the lands were reduced to
chaos by a universal eruption of tremendous vol-
canoes; and then a period of comparative quiet fol-
lowed, during which new seas were formed, and new
life perhaps began to flourish in the lunar world, only
to end in another cataclysm, which finally put a term
to the existence of the moon as a life-supporting world.

229

CURIOSITIES OF THE SKY

Suppose we examine two more of Mr. Ritchey's
illuminating photographs, and, first, the one showing
the crater Theophilus and its surroundings. We have
spoken of Theophilus before, citing the facts that it is
sixty-four miles in diameter and eighteen thousand feet
deep. It will be noticed that it has two brother
giants — Cyrillus the nearer, and Catharina the more
distant; but Theophilus is plainly the youngest of
the trio. Centuries, and perhaps thousands of years,
must have elapsed between the periods of their up-
heaval, for the two older craters are partly filled
with debris, while it is manifest at a glance that
when the southeastern wall of Theophilus was formed,
it broke away and destroyed a part of the more
ancient ring of Cyrillus. There is no more tremendous
scene on the moon than this ; viewed with a powerful
telescope, it is absolutely appalling.

The next photograph shows, if possible, a still
wilder region. It is the part of the moon lying be-
tween Tycho and the south pole. Tycho is seen in
the lower left-hand part of the picture. To the right,
at the edge of the illuminated portion of the moon,
are the crater-rings, Longomontanus and Wilhelm I.,
the former being the larger. Between them are to
be seen the ruins of two or three more ancient craters
which, together with portions of the walls of Wilhelm
I. and Longomontanus, have been honeycombed
with smaller craters. The vast crateriform depression
above the centre of the picture is Clavius, an un-
rivalled wonder of lunar scenery, a hundred and
forty-two miles in its greatest length, while its whole
immense floor has sunk two miles below the general

230

T.UNAR CRATER THEOPHILUS AND SURROUNDING REGION

THE WRECKING OF THE MOON

surface of the moon outside the ring. The monstrous
shadow-filled cavity above Clavius toward the right
is Blancanus, whose aspect here gives a good idea of
the appearance of these chasms when only their rims
are in the sunlight. But observe the indescribable
savagery of the entire scene. It looks as though
the spirit of destruction had gone mad in this spot.
The mighty craters have broken forth one after an-
other, each rending its predecessor; and when their
work was finished, a minor but yet tremendous out-
break occurred, and the face of the moon was gored
and punctured with thousands of smaller craters.
These relatively small craters (small, however, only in
a lunar sense, for many of them would appear gigantic
on the earth) recall once more the theory of meteoric
impact. It does not seem impossible that some of
them may have been formed by such an agency.

One would not wish for our planet such a fate as
that which has overtaken the moon, but we cannot
be absolutely sure that something of the kind may
not be in store for it. We really know nothing of
the ultimate causes of volcanic activity, and some
have suggested that the internal energies of the earth
may be accumulating instead of dying out, and may
never yet have exhibited their utmost destructive
power. Perhaps the best assurance that we can find
that the earth will escape the catastrophe that has
overtaken its satellite is to be found in the relatively
great force of its gravitation. The moon has been
the victim of its weakness; given equal forces, and the
earth would be the better able to withstand them.
It is significant, in connection with these considera-

233

CURIOSITIES OF THE SKY

tions, that the little planet Mercury, which seems
also to have parted with its air and water, shows to
the telescope some indications that it is pitted with
craters resembling those that have torn to pieces the
face of the moon.

Upon the whole, after studying the dreadful lunar
landscapes, one cannot feel a very enthusiastic sym-
pathy with those who are seeking indications of the
continued existence of some kind of life on the moon;
such a world is better without inhabitants. It has
met its fate; let it go! Fortunately, it is not so near
that it cannot hide its scars and appear beautiful —
except when curiosity impels us to look with the
penetrating eyes of the astronomer.

MARE CRISIUM

XIII

THE GREAT MARS PROBLEM

I ET any thoughtful person who is acquainted with
L/the general facts of astronomy look up at the
heavens some night when they appear in their great-
est splendor, and ask himself what is the strong-
est impression that they make upon his mind. He
may not find it easy to frame an answer, but when he
has succeeded it will probably be to the effect that
the stars give him an impression of the universality
of intelligence; they make him feel, as the sun and
the moon cannot do, that his world is not alone ; that
all this was not made simply to form a gorgeous
canopy over the tents of men. If he is of a devout
turn of mind, he thinks, as he gazes into those fathom-
less deeps and among those bewildering hosts, of the
infinite multitude of created beings that the Al-
mighty has taken under his care. The narrow ideas
of the old geocentric theology, which made the earth
God's especial footstool, and man his only rational
creature, fall away from him like a veil that had
obscured his vision; they are impossible in the pres-
ence of what he sees above. Thus the natural ten-
dency, in the light of modern progress, is to regard
the universe as everywhere filled with life.

237

CURIOSITIES OF THE SKY

But science, which is responsible for this broaden-
ing of men's thoughts concerning the universality of
life, itself proceeds to set limits. Of spiritual exist-
ences it pretends to know nothing, but as to physical
beings, it declares that it can only entertain the sup-
position of their existence where it finds evidence of
an environment suited to their needs, and such en-
vironment may not everywhere exist. Science,
though repelled by the antiquated theological con-
ception of the supreme isolation of man among created
beings, regards with complacency the probability
that there are regions in the universe where no organic
life exists, stars which shine upon no inhabited
worlds, and planets which nourish no animate creat-
ures. The astronomical view of the universe is that
it consists of matter in every stage of evolution:
some nebulous and chaotic; some just condensing
into stars (suns) of every magnitude and order; some
shaped into finished solar bodies surrounded by de-
pendent planets; some forming stars that perhaps
have no planets, and will have none ; some constitut-
ing suns that are already aging, and will soon lose
their radiant energy and disappear; and some ag-
gregated into masses that long ago became inert,
cold, and rayless, and that can only be revivified by
means about which we can form conjectures, but of
which we actually know nothing.

As with the stars, so with the planets, which are
the satellites of stars. All investigations unite to
tell us that the planets are not all in the same state
of development. As some are large and some small,
so some are, in an evolutionary sense, young, and

238

THE GREAT MARS PROBLEM

some old. As they depend upon the suns around
which they revolve for their light, heat, and other
forms of radiant energy, so their condition varies
with their distance from those suns. Many may
never arrive at a state suitable for the maintenance
of life upon their surfaces; some which are not at
present in such a state may attain it later; and the
forms of life themselves may vary with the peculiar
environment that different planets afford. Thus we
see that we are not scientifically justified in affirming
that life is ubiquitous, although we are thus justified
in saying that it must be, in a general sense, universal.
We might liken the universe to a garden known to
contain every variety of plant. If on entering it we
see no flowers, we examine the species before us and
find that they are not of those which bloom at this
particular season, or perhaps they are such as never
bear flowers. Yet we feel no doubt that we shall find
flowers somewhere in the garden, because there are
species which bloom at this season, and the garden
contains all varieties.

While it is tacitly assumed that there are planets
revolving around other stars than the sun, it would
be impossible for us to see them with any telescope
yet invented, and no instrument now in the
posession of astronomers could assure us of their
existence; so the only planetary system of which
we have visual knowledge is our own. Excluding
the asteroids, which could not from any point of
view be considered as habitable, we have in the solar
system eight planets of various sizes and situated at
various distances from the sun. Of these eight we

239

CURIOSITIES OF THE SKY

know that one, the earth, is inhabited. The ques-
tion, then, arises: Are there any of the others which
are inhabited or habitable ? Since it is our intention
to discuss the habitability of only one of the seven
to which the question applies, the rest may be dis-
missed in a few words. The smallest of them, and
the nearest to the sun, is Mercury, which is regarded
as uninhabitable because it has no perceptible supply
of water and air, and because, owing to the extraor-
dinary eccentricity of its orbit, it is subjected to
excessive and very rapid alterations in the amount
of solar heat and light poured upon its surface, such
alterations being inconsistent with the supposition
that it can support living beings. Even its average
temperature is more than six and a half times that
prevailing on the earth! Another circumstance
which militates against its habitability is that, ac-
cording to the results of the best telescopic studies,
it always keeps the same face toward the sun, so that
one half of the planet is perpetually exposed to the
fierce solar rays, and the other half faces the un-
mitigated cold of open space. Venus, the next in
distance from the sun, is almost the exact twin of
the earth in size, and many arguments may be urged
in favor of its habitability, although it is suspected
of possessing the same peculiarity as Mercury, in
always keeping the same side sunward. Unfortu-
nately its atmosphere appears to be so dense that
no permanent markings on its surface are certainly
visible, and the question of its actual condition must,
for the present, be left in abeyance. Mars, the first
planet more distant from the sun than the earth, is

THE GREAT MARS PROBLEM

the special subject of this chapter, and will be de-
scribed and discussed a few lines further on. Jupiter,
Saturn, Uranus, and Neptune, the four giant planets,
all more distant than Mars, and each more distant
than the other in the order named, are all regarded
as uninhabitable because none of them appears to
possess any degree of solidity. They may have solid
or liquid nuclei, but exteriorly they seem to be mere
balls of cloud. Of course, one can imagine what he
pleases about the existence of creatures suited to the
physical constitution of such planets as these, but
they must be excluded from the category of habitable
worlds in the ordinary sense of the term. We go
back, then, to Mars.

It will be best to begin with a description of the
planet. Mars is 4230 miles in diameter; its surface
is not much more than one-quarter as extensive as
that of the earth (.285). Its mean distance from the
sun is 141,500,000 miles, 48,500,000 miles greater than
that of the earth. Since radiant energy varies in-
versely as the square of distance, Mars receives less
than half as much solar light and heat as the earth
gets. Mars' year (period of revolution round the
sun) is 687 days. Its mean density is 71 per cent,
of the earth's, and the force of gravity on its surface
is 38 per cent, of that on the surface of the earth;
i.e., a body weighing one hundred pounds on the
earth would, if transported to Mars, weigh but thirty-
eight pounds. The inclination of its equator to the
plane of its orbit differs very little from that of the
earth's equator, and its axial rotation occupies 24
hours 37 minutes; so that the length of day and

241

CURIOSITIES OF THE SKY

night, and the extent of the seasonal changes on
Mars, are almost precisely the same as on the earth.
But owing to the greater length of its year, the sea-
sons of Mars, while occurring in the same order, are
almost twice as long as ours. The surface of the
planet is manifestly solid, like that of our globe, and
the telescope reveals many permanent markings on
it, recalling the appearance of a globe on which geo-
graphical features have been represented in reddish
and dusky tints. Around the poles are plainly to
be seen rounded white areas, which vary in extent
with the Martian seasons, nearly vanishing in sum-
mer and extending widely in winter. The most
recent spectroscopic determinations indicate that
Mars has an atmosphere perhaps as dense as that to
be found on our loftiest mountain peaks, and there
is a perceptible amount of watery vapor in this
atmosphere. The surface of the planet appears to
be remarkably level, and it has no mountain ranges.
No evidences of volcanic action have been discovered
on Mars. The dusky and reddish areas were re-
garded by the early observers as respectively seas
and lands, but at present it is not believed that there
are any bodies of water on the planet. There has
never been much doubt expressed that the white
areas about the poles represent snow.

It will be seen from this brief description that many
remarkable resemblances exist between Mars and the
earth, and there is nothing wonderful in the fact that
the question of the habitability of the former has be-
come one of extreme and wide-spread interest, giving
rise to the most diverse views, to many extraordinary

242

THE GREAT MARS PROBLEM

speculations, and sometimes to regrettably heated
controversy. The first champion of the habitability
of Mars was Sir William Herschel, although even
before his time the idea had been suggested. He
was convinced by the revelations of his telescopes,
continually increasing in power, that Mars was more
like the earth than any other planet. He could not
resist the testimony of the polar snows, whose sug-
gestive conduct was in such striking accord with what
occurs upon the earth. Gradually, as telescopes im-
proved and observers increased in number, the prin-
cipal features of the planet were disclosed and charted,
and "areography," as the geography of Mars was
called, took its place among the recognized branches
of astronomical study. But it was not before 1877
that a fundamentally new discovery in areography
gave a truly sensational turn to speculation about
life on "the red planet." In that year Mars made
one of its nearest approaches to the earth, and was
so situated in its orbit that it could be observed to
great advantage from the northern hemisphere of
the earth. The celebrated Italian astronomer, Schia-
parelli, took advantage of this opportunity to make
a trigonometrical survey of the surface of Mars — as
coolly and confidently as if he were not taking his
sights across a thirty-five-million-mile gulf of empty
space — and in the course of this survey he was aston-
ished to perceive that the reddish areas, then called
continents, were crossed in many directions by narrow,
dusky lines, to which he gave the suggestive name of
"canals." Thus a kind of firebrand was cast into
the field of astronomical speculation, which has ever

243

CURIOSITIES OF THE SKY

since produced disputes that have sometimes ap-
proached the violence of political faction. At first
the accuracy of Schiaparelli's observations was con-
tested; it required a powerful telescope, and the
most excellent "seeing," to render the enigmatical
lines visible at all, and many searchers were unable to
detect them. But Schiaparelli continued his studies
in the serene sky of Italy, and produced charts of the
gridironed face of Mars containing so much aston-
ishing detail that one had either to reject them in
toto or to confess that Schiaparelli was right. As
subsequent favorable oppositions of Mars occurred,
other observers began to see the "canals" and to
confirm the substantial accuracy of the Italian as-
tronomer's work, and finally few were found who
would venture to affirm that the "canals" did not
exist, whatever their meaning might be.

When Schiaparelli began his observations it was
generally believed, as we have said, that the dusky
areas on Mars were seas, and since Schiaparelli thought
that the "canals" invariably began and ended at the
shores of the "seas," the appropriateness of the title
given to the lines seemed apparent. Their artificial
character was immediately assumed by many, be-
cause they were too straight and too suggestively
geometrical in their arrangement to permit the con-
clusion that they were natural watercourses. A
most surprising circumstance noted by Schiaparelli
was that the "canals" made their appearance after
the melting of the polar snow in the corresponding
hemisphere had begun, and that they grew darker,
longer, and more numerous in proportion as the polar

244

THE GREAT MARS PROBLEM

liquidation proceeded. Another very puzzling ob-
servation was that many of them became double as
the season advanced; close beside an already exist-
ing " canal,'* and in perfect parallelism with it, an-
other would gradually make its appearance. That
these phenomena actually existed and were not
illusions was proved by later observations, and to- '
day they are seen whenever Mars is favorably situated
for observation.

In the closing decade of the nineteenth century,
Mr. Percival Lowell took up the work where Schia-
parelli had virtually dropped it, and soon added a
great number of " canals " to those previously known,
so that in his charts the surface of the wonderful
little planet appears covered as with a spider's web,
the dusky lines criss-crossing in every direction, with
conspicuous knots wherever a number of them come
together. Mr. Lowell has demonstrated that the areas
originally called seas, and thus named on the earlier
charts, are not bodies of water, whatever else they
may be. He has also found that the mysterious lines
do not, as Schiaparelli supposed, begin and end at
the edges of the dusky regions, but often continue
on across them, reaching in some cases far up into
the polar regions. But Schiaparelli was right in his
observation that the appearance of the "canals" is
synchronous with the gradual disappearance of the
polar snows, and this fact has become the basis of
the most extraordinary theory that the subject of
life in other worlds has ever given birth to.

Now, the effect of such discoveries, as we have
related, depends upon the type of mind to whose

247

CURIOSITIES OF THE SKY

attention they are called. Many are content to ac-
cept them as strange and inexplicable at present,
and to wait for further light upon them; others in-
sist upon an immediate inquiry concerning their
probable nature and meaning. Such an inquiry can
only be based upon inference proceeding from analogy.
Mars, say Mr. Lowell and those who are of his opin-
ion, is manifestly a solidly incrusted planet like the
earth; it has an atmosphere, though one of great
rarity; it has water vapor, as the snows in them-
selves prove ; it has the alternation of day and night,
and a succession of seasons closely resembling those
of the earth; its surface is suggestively divided into
regions of contrasting colors and appearance, and
upon that surface we see an immense number of lines
geometrically arranged, with a system of symmetri-
cal intersections where the lines expand into circular
and oval areas — and all connected with the annual
melting of the polar snows in a way which irresistibly
suggests the interference of intelligence directed to
a definite end. Why, with so many concurrent cir-
cumstances to support the hypothesis, should we not
regard Mars as an inhabited globe?

But the differences between Mars and the earth are
in many ways as striking as their resemblances.
Mars is relatively small ; it gets less than half as much
light and heat as we receive; its atmosphere is so
rare that it would be distressing to us, even if we
could survive in it at all; it has no lakes, rivers, or
seas ; its surface is an endless prairie ; and its ' ' canals ' '
are phenomena utterly unlike anything on the earth.
Yet it is precisely upon these divergences between

348

THE GREAT MARS PROBLEM

the earth and Mars, this repudiation of terrestrial
standards, that the theory of "life on Mars," for
which Mr. Lowell is mainly responsible, is based.
Because Mars is smaller than the earth, we are told
it must necessarily be more advanced in planetary
evolution, the underlying cause of which is the grad-
ual cooling and contraction of the planet's mass.
Mars has parted with its internal heat more rapidly
than the earth; consequently its waters and its at-
mosphere have been mostly withdrawn by chemical
combinations, but enough of both yet remain to
render life still possible on its surface. As the globe
of Mars is evolutionally older than that of the earth,
so its forms of organic life may be proportionally
further advanced, and its inhabitants may have
attained a degree of cultivated intelligence much
superior to what at present exists upon the earth.
Understanding the nature and the causes of the
desiccation of their planet, and possessing engineer-
ing science and capabilities far in advance of ours,
they may be conceived to have grappled with the
stupendous problem of keeping their world in a
habitable condition as long as possible. Supposing
them to have become accustomed to live in their
rarefied atmosphere (a thing not inconceivable, since
men can live for a time at least in air hardly less
rare), the most pressing problem for them is that of
a water-supply, without which plant life cannot exist,
while animal life in turn depends for its existence
upon vegetation. The only direction in which they
can seek water is that of the polar regions, where it is
alternately condensed into snow and released in the

249

CURIOSITIES OF THE SKY

liquid form by the effect of the seasonal changes. It
is, then, to the annual melting of the polar snow-fields
that the Martian engineers are supposed to have
recourse in supplying the needs of their planet, and
thus providing the means of prolonging their own
existence. It is imagined that they have for this
purpose constructed a stupendous system of irriga-
tion extending over the temperate and equatorial
regions of the planet. The "canals" represent the
lines of irrigation, but the narrow streaks that we see
are not the canals themselves, but the irrigated bands
covered by them. Their dark hue, and their gradual
appearance after the polar melting has begun, are
due to the growth of vegetation stimulated by the
water. The rounded areas visible where several
"canals" meet and cross are called by Mr. Lowell
"oases." These are supposed to be the principal
centres of population and industry. It must be con-
fessed that some of them, with their complicated
systems of radiating lines, appear to answer very well
to such a theory. No attempt to explain them by
analogy with natural phenomena on the earth has
proved successful.

But a great difficulty yet remains: How explain
the seemingly miraculous powers of the supposed
engineers? Here recourse is had once more to the
relative smallness of the planet. We have remarked
that the force of gravity on Mars is only thirty-eight
per cent, of that on the earth. A steam -shovel
driven by a certain horse-power would be nearly
three times as effective there as here. A man of our
stature on Mars would find his effective strength in-

250

THE GREAT MARS PROBLEM

creased in the same proportion. But just because of
the slight force of gravity there, a Martian might
attain to the traditional stature of Goliath without
rinding his own weight an encumbrance to his activity,
while at the same time his huge muscles would come
into unimpeded play, enabling him single-handed to
perform labors that would be impossible to a whole
gang of terrestrial workmen. The effective powers
of huge machines would be increased in the same
way; and to all this must be added the fact that the
mean density of the materials of which Mars is com-
posed is much less than that of the constituents of
the earth. Combining all these considerations, it
becomes much less difficult to conceive that public
works might be successfully undertaken on Mars
which would be hopelessly beyond the limits of hu-
man accomplishment.

Certain other difficulties have also to be met; as,
for instance, the relative coldness of the climate of
Mars. At its distance it gets considerably less than
half as much light and heat as we receive. In addi-
tion to this, the rarity of its atmosphere would
naturally be expected to decrease the effective tem-
perature at the planet's surface, since an atmosphere
acts somewhat like the glass cover of a hot-house in
retaining the solar heat which has penetrated it. It
has been calculated that, unless there are mitigating
circumstances of which we know nothing, the aver-
age temperature at the surface of Mars must be far
below the freezing-point of water. To this it is re-
plied that the possible mitigating circumstances
spoken of evidently exist in fact, because we can see

CURIOSITIES OF THE SKY

that the watery vapor condenses into snow around
the poles in winter, but melts again when summer
comes. The mitigating agent may be supposed to
exist in the atmosphere where the presence of cer-
tain gases would completely alter the temperature
gradients.

It might also be objected that it is inconceivable
that the Martian engineers, however great may be
their physical powers, and however gigantic the
mechanical energies under their control, could force
water in large quantities from the poles to the equator.
This is an achievement that measures up to the cos-
mical standard. It is admitted by the champions of
the theory that the difficulty is a formidable one;
but they call attention to the singular fact that on
Mars there can be found no chains of mountains, and
it is even doubtful if ranges of hills exist there. The
entire surface of the planet appears to be almost
"as smooth as a billiard ball," and even the broad
regions which were once supposed to be seas apparent-
ly lie at practically the same level as the other parts,
since the "canals" in many cases run uninterrupted-
ly across them. Lowell's idea is that these sombre
areas may be expanses of vegetation covering ground
of a more or less marshy character, for while the
largest of them appear to be permanent, there are
some which vary coincidently with the variations of
the canals.

As to the kind of machinery employed to force the
water from the poles, it has been conjectured that it
may have taken the form of a gigantic system of
pumps and conduits; and since the Martians are

252

THE GREAT MARS PROBLEM

assumed to be so far in advance of us in their mastery
of scientific principles, the hypothesis will at least not
be harmed by supposing that they have learned to
harness forces of nature whose very existence in a
manageable form is yet unrecognized on the earth.
If we wish to let the imagination loose, we may con-
jecture that they have conquered the secret of those
intra-atomic forces whose resistless energy is begin-
ning to become evident to us, but the possibility of
whose utilization remains a dream, the fulfilment of
which nobody dares to predict.

Such, in very brief form, is the celebrated theory
of Mars as an inhabited world. It certainly capti-
vates the imagination, and if we believe it to repre-
sent the facts, we cannot but watch with the deepest
sympathy this gallant struggle of an intellectual race
to preserve its planet from the effects of advancing
age and death. We may, indeed, wonder whether
our own humanity, confronted by such a calamity,
could be counted on to meet the emergency with
equal stoutness of heart and inexhaustibleness of
resource. Up to the present time we certainly have
shown no capacity to confront Nature toe to toe, and
to seize her by the shoulders and turn her round
when she refuses to go our way. If we could get into
wireless telephonic communication with the Martians
we might learn from their own lips the secret of their
more than " Roman recovery."
sa

XIV

THE RIDDLE OF THE ASTEROIDS

DETWEEN the orbits of Mars and Jupiter re-
JD volves the most remarkable system of little
bodies with which we are acquainted — the Asteroids,
or Minor Planets. Some six hundred are now known,
and they may actually number thousands. They
form virtually a ring about the sun. The most strik-
ing general fact about them is that they occupy the
place in the sky which should be occupied, according
to Bode's Law, by a single large planet. This fact,
as we shall see, has led to the invention of one of the
most extraordinary theories in astronomy — viz., that
of the explosion of a world!

Bode's Law, so-called, is only an empiric formula,
but until the discovery of Neptune it accorded so
well with the distances of the planets that astron-
omers were disposed to look upon it as really repre-
senting some underlying principle of planetary dis-
tribution. They were puzzled by the absence of a
planet in the space between Mars and Jupiter, where
the "law" demanded that there should be one, and
an association of astronomers was formed to search
for it. There was a decided sensation when, in 1801,
Piazzi, of Palermo, announced that he had found a

254

THE RIDDLE OF THE ASTEROIDS

little planet which apparently occupied the place in
the system which belonged to the missing body.
He named it Ceres, and it was the first of the Asteroids.
The next year Olbers, of Bremen, while looking for
Ceres with his telescope, stumbled upon another small
planet which he named Pallas. Immediately he was
inspired with the idea that these two planets were
fragments of a larger one which had formerly occu-
pied the vacant place in the planetary ranks, and he
predicted that others would be found by searching
in the neighborhood of the intersection of the orbits
of the two already discovered. This bold prediction
was brilliantly fulfilled by the finding of two more —
Juno in 1804, and Vesta in 1807. Olbers would seem
to have been led to the invention of his hypothesis
of a planetary explosion by the faith which astron-
omers at that time had in Bode's Law. They ap-
pear to have thought that several planets revolving
in the gap where the "law" called for but one could
only be accounted for upon the theory that the
original one had been broken up to form the several.
Gravitation demanded that the remnants of a planet
blown to pieces, no matter how their orbits might
otherwise differ, should all return at stated periods
to the point where the explosion had occurred ; hence
Olbers' prediction that any asteroids that might sub-
sequently be discovered would be found to have a
common point of orbital intersection. And curiously
enough all of the first asteroids found practically
answered to this requirement. Olbers' theory seemed
to be established.

After the first four, no more asteroids were found

255

CURIOSITIES OF THE SKY

until 1845, when one was discovered; then, in 1847,
three more were added to the list; and after that
searchers began to pick them up with such rapidity
that by the close of the century hundreds were
known, and it had become almost impossible to keep
track of them. The first four are by far the largest
members of the group, but their actual sizes remained
unknown until less than twenty years ago. It was
long supposed that Vesta was the largest, because it
shines more brightly than any of the others; but
finally, in 1895, Barnard, with the Lick telescope,
definitely measured their diameters, and proved to
everybody's surprise that Ceres is really the chief,
and Vesta only the third in rank. His measures are
as follows: Ceres, 477 miles; Pallas, 304 miles;
Vesta, 239 miles; and Juno, 120 miles. They differ
greatly in the reflective power of their surfaces, a
fact of much significance in connection with the
question of their origin. Vesta is, surface for surface,
rather more than three times as brilliant as Ceres,
whence the original mistake about its magnitude.

Nowadays new asteroids are found frequently by
photography, but physically they are most insignifi-
cant bodies, their average diameter probably not ex-
ceeding twenty miles, and some are believed not to
exceed ten. On a planet only ten miles in diameter,
assuming the same mean density as the earth's,
which is undoubtedly too much, the force of gravity
would be so slight that an average man would not
weigh more than three ounces, and could jump off
into space whenever he liked.

Although the asteroids all revolve around the sun

256

THE RIDDLE OF THE ASTEROIDS

in the same direction as that pursued by the major
planets, their orbits are inclined at a great variety
of angles to the general plane of the planetary system,
and some of them are very eccentric — almost as much
so as the orbits of many of the periodic comets. It
has even been conjectured that the two tiny moons
of Mars and the four smaller satellites of Jupiter
may be asteroids gone astray and captured by those
planets. Two of the asteroids are exceedingly re-
markable for the shapes and positions of their orbits ;
these are Eros, discovered in 1898, and T. G., 1906,
found eight years later. The latter has a mean dis-
tance from the sun slightly greater than that of
Jupiter, while the mean distance of Eros is less than
that of Mars. The orbit of Eros is so eccentric that
at times it approaches within 15,000,000 miles of the
earth, nearer than any other regular member of the
solar system except the moon, thus affording an un-
rivalled means of measuring the solar parallax. But
for our present purpose the chief interest of Eros lies
in its extraordinary changes of light.

These changes, although irregular, have been ob-
served and photographed many times, and there
seems to be no doubt of their reality. Their signifi-
cance consists in their possible connection with the
form of the little planet, whose diameter is generally
estimated at not more than twenty miles. Von
Oppolzer found, in 1901, that Eros lost three-fourths
of its brilliancy once in every two hours and thirty-
eight minutes. Other observers have found slightly
different periods of variability, but none as long as
three hours. The most interesting interpretation

257

CURIOSITIES OF THE SKY

that has been offered of this phenomenon is that it is
due to a great irregularity of figure, recalling at once
Gibers' hypothesis. According to some, Eros may
be double, the two bodies composing it revolving
around each other at very close quarters; but a more
striking, and it may be said probable, suggestion is
that Eros has a form not unlike that of a dumb-bell,
or hour-glass, turning rapidly end over end so that
the area of illuminated surface presented to our eyes
continually changes, reaching at certain times a
minimum when the amount of light that it reflects
toward the earth is reduced to a quarter of its maxi-
mum value. Various other bizarre shapes have been
ascribed to Eros, such, for instance, as that of a
flat stone revolving about one of its longer axes, so
that sometimes we see its face and sometimes its
edge.

All of these explanations proceed upon the as-
sumption that Eros cannot have a simple globular
figure like that of a typical planet, a figure which is
prescribed by the law of gravitation, but that its
shape is what may be called accidental; in a word,
it is a, fragment, for it seems impossible to believe that
a body formed in interplanetary space, either through
nebular condensation or through the aggregation of
particles drawn together by their mutual attractions,
should not be practically spherical in shape. Nor is
Eros the only asteroid that gives evidence by varia-
tions of brilliancy that there is something abnormal
in its constitution; several others present the same
phenomenon in varying degrees. Even Vesta was
regarded by Olbers as sufficiently variable in its light

THE RIDDLE OF THE ASTEROIDS

to warrant the conclusion that it was an angular mass
instead of a globe. Some of the smaller ones show
very notable variations, and all in short periods, of
three or four hours, suggesting that in turning about
one of their axes they present a surface of variable
extent toward the sun and the earth.

The theory which some have preferred that the
variability of light is due to the differences of reflect-
ive power on different parts of the surface would,
if accepted, be hardly less suggestive of the
origin of these little bodies by the breaking up of a
larger one, because the most natural explanation of
such differences would seem to be that they arose
from variations in the roughness or smoothness of
the reflecting surface, which would be characteristic
of fragmentary bodies. In the case of a large planet
alternating expanses of land and water, or of vegeta-
tion and desert, would produce a notable variation
in the amount of reflection, but on bodies of the size
of the asteroids neither water nor vegetation could
exist, and an atmosphere would be equally im-
possible.

One of the strongest objections to Olbers' hypoth-
esis is that only a few of the first asteroids discovered
travel in orbits which measurably satisfy the re-
quirement that they should all intersect at the point
where the explosion occurred. To this it was at first
replied that the perturbations of the asteroidal orbits,
by the attractions of the major planets, would soon
displace them in such a manner that they would
cease to intersect. One of the first investigations
tmclertaken by the late Prof. Simon Newcomb was

259

CURIOSITIES OF THE SKY

directed to the solution of this question, and he ar-
rived at the conclusion that the planetary perturba-
tions could not explain the actual situation of the
asteroidal orbits. But afterward it was pointed out
that the difficulty could be avoided by supposing
that not one but a series of explosions had produced
the asteroids as they now are. After the primary
disruption the fragments themselves, according to
this suggestion, may have exploded, and then the
resulting orbits would be as "tangled" as the heart
could wish. This has so far rehabilitated the
explosion theory that it has never been entirely
abandoned, and the evidence which we have just
cited of the probably abnormal shapes of Eros and
other asteroids has lately given it renewed life. It
is a subject that needs a thorough rediscussion.

We must not fail to mention, however, that there
is a rival hypothesis which commends itself to many
astronomers — viz., that the asteroids were formed out
of a relatively scant ring of matter, situated between
Mars and Jupiter and resembling in composition the
immensely more massive rings from which, according
to Laplace's hypothesis, the planets were born. It
is held by the supporters of this theory that the at-
traction of the giant Jupiter was sufficient to prevent
the small, nebulous ring that gave birth to the
asteroids from condensing like the others into a single
planet.

But if we accept the explosion theory, with its cor-
ollary that minor explosions followed the principal
one, we have still an unanswered question before us:
What caused the explosions? The idea of a world

THE RPDDLE OF THE ASTEROIDS

blowing up is too Titanic to be shocking; it rather
amuses the imagination than seriously impresses it;
in a word, it seems essentially chimerical. We can by
no appeal to experience form a mental picture of
such an occurrence. Even the moon did not blow
up when it was wrecked by volcanoes. The ex-
plosive nebulas and new stars are far away in space,
and suggest no connection with such a catastrophe
as the bursting of a planet into hundreds of pieces.
We cannot conceive of a great globe thousands of
miles in diameter resembling a pellet of gunpowder
only awaiting the touch of a match to cause its sud-
den disruption. Somehow the thought of human
agency obtrudes itself in connection with the word
" explosion," and we smile at the idea that giant
powder or nitro-glycerine could blow up a planet.
Yet it would only need enough of them to do it.

After all, we may deceive ourselves in thinking, as
we are apt to do, that explosive energies lock them-
selves up only in small masses of matter. There are
many causes producing explosions in nature | every
volcanic eruption manifests the activity of some of
them. Think of the giant power of confined steam;
if enough steam could be suddenly generated in the
centre of the earth by a downpour of all the waters
of the oceans, what might not the consequences be
for our globe? In a smaller globe, and it has never
been estimated that the original asteroid was even
as large as the moon, such a catastrophe would, per-
haps, be more easily conceivable; but since we are
compelled in this case to assume that there was a
series of successive explosions, steam would hardly

261

CURIOSITIES OF THE SKY

answer the purpose; it would be more reasonable
to suppose that the cause of the explosion was some
kind of chemical reaction, or something affecting the
atoms composing the exploding body. Here Dr.
Gustav Le Bon comes to our aid with a most startling
suggestion, based on his theory of the dissipation of
intra-atomic energy. It will be best to quote him
at some length from his book on The Evolution of
Forces.

"It does not seem at first sight,'* says Doctor Le
Bon, "very comprehensible that worlds which ap-
pear more and more stable as they cool could become
so unstable as to afterward dissociate entirely. To
explain this phenomenon, we will inquire whether
astronomical observations do not allow us to witness
this dissociation.

"We know that the stability of a body in motion,
such as a top or a bicycle, ceases to be possible when
its velocity of rotation descends below a certain
limit. Once this limit is reached it loses its stability
and falls to the ground. Prof. J. J. Thomson even
interprets radio-activity in this manner, and points
out that when the speed of the elements composing
the atoms descends below a certain limit they be-
come unstable and tend to lose their equilibria.
There would result from this a commencement of
dissociation, with diminution of their potential energy
and a corresponding increase of their kinetic energy
sufficient to launch into space the products of intra-
atomic disintegration.

"It must not be forgotten that the atom being an
enormous reservoir of energy is by this very fact

962

THE RIDDLE OF THE ASTEROIDS

comparable with explosive bodies. These last re-
main inert so long as their internal equilibria are
undisturbed. So soon as some cause or other modi-
fies these, they explode and smash everything around
them after being themselves broken to pieces.

"Atoms, therefore, which grow old in consequence
of the diminution of a part of their intra-atomic
energy gradually lose their stability. A moment,
then, arrives when this stability is so weak that the
matter disappears by a sort of explosion more or less
rapid. The bodies of the radium group offer an
image of this phenomenon — a rather faint image, how-
ever, because the atoms of this body have only
reached a period of instability when the dissociation
is rather slow. It probably precedes another and
more rapid period of dissociation capable of produc-
ing their final explosion. Bodies such as radium,
thorium, etc., represent, no doubt, a state of old age
at which all bodies must some day arrive, and which
they already begin to manifest in our universe, since
all matter is slightly radio-active. It would suffice
for the dissociation to be fairly general and fairly
rapid for an explosion to occur in a world where it
was manifested.

" These theoretical considerations find a solid sup-
port in the sudden appearances and disappearances
of stars. The explosions of a world which produce
them reveal to us, perhaps, how the universes perish
when they become old.

"As astronomical observations show the relative
frequency of these rapid destructions, we may ask
ourselves whether the end of a universe by a sudden

263

CURIOSITIES OF THE SKY

explosion after a long period of old age does not
represent its most general ending."

Here, perhaps, it will be well to stop, since, entran-
cing as the subject may be, we know very little about
it, and Doctor Le Bon's theory affords a limitless
field for the reader's imagination.

INDEX

AEORLITES, study of, 197.

Alcor, 58, 59.

Alcyone, 37, 41, 42.

Aldebaran, 62, 86.

Alioth, 58, 59, 60.

Alpha Centauri, 46, 66.

Alpha Herculis, 86.

Alnilam, 64.

Alnita, 64.

Anderson, Rev. Doctor, dis-
covers Nova Persei, 75.

Andromeda Nebula, 75, 91, 99,
100, 103, 104, 192.

Antares, 86.

Arcturus, 8, 44, 46, 66, 68.

Arrhenius, Svante, theory, 139,
142, 143, 154, 158, 160, 184.

Aso San, crater, 219.

Asteroids, the, 29, 252.

Atlas, 37.

Auriga, 75.

Aurora Australis, 148.

Aurora Borealis, 147, 148, 154,
157, 160.

BAILY, FRANCIS, quoted, 117,

118.

Belt, Orion's, 64.
Benetnasch, 58, 59, 60.
Betelgeuse, 64, 86.
Biela's comet, 180, 191, 192,

195.

Brooks' comet, 176, 181.
" Black stone," the, 196.
Bode's Law, 254, 255.
Bredichin, researches, 184.

CANCER, 55.
Canopus, 68.
Canyon Diablo meteors, 202,

204.

Capella, 75, 76.
Cassiopeia, 24, 56, 61, 69.
Catharina, crater, 230.
Centaurus, 14, 30.
Ceres, 255, 256.
Cetus, 86, 99.
Chamberlin, Professor, theory,

107.

Chi Persei, 24.
Clavius, crater, 230.
Clerke, Agnes M., quoted, 8,

I52-

Coal-sack, the, 2, 3, 4, 7, 13.

Comet, Halley's, 165; Swift's,
167; phenomena, 169; ap-
proach to the sun, 170; of
1811, 171; of 1882, 171, 174,
175; their light, 171; of 1908,
172; of 1729, 172; of 1843,
173, 174, 175; of 1858, 173;
of 1861, 173; of 1880, 174;
of 1668, 175; and photog-
raphy, 176; Brooks', 176;
Daniels', 176; of 1770, 179;
family, 180; Biela's, 180,
191, 192, 195; tails, 183, 184;
of 1744, 185; disintegration,
191.

Comstock, George C., theory,
20, 33.

Coon Butte Meteorite, 202, 204,
211, 212.

265

CURIOSITIES OF THE SKY

Corona, 113, 144, 117, 118, 119,
124, 125, 130, 138.

Coronium, 124.

Corvus, 62.

Craters, lunar, 216, 219-221;
Tycho, 216, 219; Theophilus,
219, 230; Cyrillus, 230; Catha-
rina, 230; Longomontanus,
230; Wilhelm I., 230; Clavius,
230.

Cygnus, 8, 38, 62, 73, 74.

Cyrillus Crater, 230.

DANIELS' comet, 176.

Delphinus, 62.

Denning, W. F., researches,
188.

Diamonds in meteorites, 202.

Donati's comet, 173, 184.

Dubhe, 58, 59, 60.

Dyson, Professor, investiga-
tions, 50, 51.

EARTH, course, 47, 49; magnet,

148, 157-

Eclipse, of the sun, 113, 114;
of 1842, 114, 117, 118; of
1900, 118, 125; of 1905, 118.

Eddington, Professor, investiga-
tions, 50.

Electra, 37.

Eros, 257, 258.

FIXED stars, 39, 40, 41.
Forbes, Prof. George, theory,
175-

GALAXY, the, 2, 3, 7, 12, 13, 17,

18, 19, 23.

" Gegenschein," 136, 137, 142.
Gemini, 62, 91.
Gilbert, W. K., on lunar craters,

221.

Great Dipper, the, 49, 57, 58.
Great Southern Comet, 174.
Great Square of Pegasus, 62.
Groombndge, 1830, motion,

43-

HALE, PROFESSOR, and sun-
spots, 123.

Halley's comet, 48, 165.

Helium, 201.

Hercules, 14, 25, 30, 46.

Herschel, Alexander, and meteor
swarms, 188.

Herschel, Sir William, observa-
tions, 2, 7, 26, 30, 243.

Hyades, 22, 62.

Hydra, 62.

IZAMAL, temples, 54, 55.

JANSSEN, PROFESSOR, theory,

84, 85.

Juno, 255, 256.
Jupiter, 29, 40, 166, 179, 180

191, 241.

KAPPA, 69.

Kapteyn, Professor, investi-
gations, 50.

Keeler, Professor, discovery, 88.
Kepler's star, 74.

LAPLACE, PROFESSOR, theory,

103, 109, in.
Le Bon, Dr. Gustav, theory, 86;

quoted, 260.
Leo, 62, 187.
Lexell's comet, 179, 180.
Longomontanus, crater - ring,

230.
Lowell, Percival, observations,

247.

Lunar Apennines, 225.
Lunar Caucasus, 225.
Lyra, 88.

MAEDLER, theory, 41.
Magellanic clouds, 24.
Magnetic storms, 126, 151, 152.
Maia, 37.

Mare Cnsium, 235.
Mare Imbrium, the, 225.
Mare Serenitatis, the, 225.
Mare Tranquilitatis, the, 229.

266

INDEX

Mars, and the Asteroids, 29;
distance from earth, 214; de-
scription, 241, 242; habit-
ability, 243; canals, 244, 247;
resemblance to the earth,
248; life on, 249-253.

Maunder, E. W., quoted, 133.

Megrez, 58, 59, 60.

Merak, 58, 59, 60.

Mercury, 234, 240.

Merope, 37.

Meteorites, study of, 197; veloc-
ity, 198, 208; stone and iron,
201, 202, 203; fall of, 203;
Peary's, 208; origin, 222.

Meteors, showers, 186, 187;
swarms, 188; November, 191;
of ancient times, 196; Canyon
Diablo, 202, 204, 211.

Milky Way, the, 2, 3, 4, 8, 9,

12, 17, l8, 19, 2O, 21, 42.

Mintaka, 64.

Mira Ceti, 86, 123.

Mizar, 58, 59, 60.

Moissan diamonds, 202.

Moon, the, distance from earth,
214; former conditions, 215;
craters of, 216, 219-221; sea-
beds, 225-229.

Morehouse's comet, 172.

Moulton, Professor, theory, 107.

NEBULA, Andromeda, 103, 104;

Orion, 103, 104.
Nebula, Trifid, 7; dark, 10, 12;

in Orion, 30; Pleiades, 34.
Nebula in Cetus, 101.
Neptune, 241.
Neptune, speed, 40.
Northern Cross, 62.
Northern Crown, 61, 63, 74, 84.
Northern Lights, 148, 158.
Nova Persei, 71, 75, 80, 81, 83,

84, 85, 86.

OLBER'S theory, 29, 253, 257.
Olmstead, Prof. Denison, and
meteors, 186, 187.

Omega Centauri, 30, 33.

Ophiuchus, 74.

Orion, 22, 37, 55, 63, 103, 104.

PALLADIUM, the, 196.

Pallas, 255, 256.

Perrine, discovery, 33.

Perseus, 24, 56, 75.

Phaed, 58, 59, 60.

Pickering, Prof. W. H., on

meteors, 211, 212.
Planetesimal Hypothesis, 107,

108, in.

Planets, the, 39, 40, 239-241.
Pleiades, 23, 34, 37, 49, 62.
Pointers, the, 59.

RHO OPHIUCHI, 10.
Rigel, 64, 86.

Rosse, Lord, Whirlpool Nebula,
88, 89; spiral nebulas, 92.

SAGITTARIUS, 4, 7.

Saturn, 191, 241.

Schiaparelli, discovery, 243, 244.

Scorpio, 4, 7, 55.

Sea of Serenity, the, 225, 226.

Sea of Showers, the, 225.

Sea of Tranquility, the, 229.

Seeliger, Professor, theory, 80.

Sickle, the, 62.

Sirius, 44, 46, 66, 86, 202.

Southern Cross, 3, 64, 65.

Spiral nebulae, 112.

Star, clouds, 23, 24, 50; swarms,
24, 25, 50; clusters, 25-34,
50; fixed, 39, 40 ; motions,
43, 44, 45, 48-52; tracks, 47,
48, 49; drift, 49, 50.

Stars, speeding, 43, 44; tem-
porary, 68, 69, 73, 74, 86.

Stones, showers, 196, 197.

Sun, eclipse, 113; surroundings,
113; prominences, 113, 119,
120, 124; spots, 123, 124, 127,
151, 154, 158; a variable star,
128.

Swan, the, 4.

267

CURIOSITIES OF THE SKY

TAURUS, 62.

Taygeta, 37.

Theophilus, crater, 219, 230.

Tidal explosion, 108.

Tides in couples, 107.

Triangulum, 96, 99, 100.

Trifid Nebula, 7.

Twins, the, 62.

Tycho, crater, 216, 219.

Tycho's Star, 69, 70, 71, 73.

URANUS, 188, 241.
Ursa Major, 57, 97, 99.

VEGA, 46, £6.
Venus, 70, 240.
Vesta, 255, 256, 258.

WHIRLPOOL NEBULA, Rosse's, 88.
Wilhelm I., crater-ring, 230.
Wolf, Rudolph, discovery, 151.

YOUNG, PROFESSOR, coronium,
124.

ZODIACAL LIGHT, the, 131-143.
Zurich Chronicles, ancient, 151.

THE END

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